Greetings Kamila,

I think the plant in the picture from Roses Loubert looks even more like what is being sold as 'Garden Party'!

Graham Stuart Thomas, Climbing Roses Old and New. 1965 edition, p41:

MULTIFLORA NANA. I have found no record of its origin, but it is available from seedsmen as R. multiflora polyantha or R. carteri, flowering in two months or so from date of sowing the seeds. A pretty, dwarf, bushy mutant or hybrid, not climbing, bearing sprays of palest pink or creamy-white single blooms all the growing season, followed by tiny red heps. The white is usually taller than the pink; both are sweetly scented.

Roger Phillips and Martin Rix, Roses. 1988 edition, p37

Rosa multiflora VAR. nana A dwarf form of R. multiflora, making a low bush up to 0.8m high, perpetual flowering, either pale pink or white, Graham Thomas records that this rose can flower in two months from seed. It is possibly a dwarf, recurrent-flowering mutant of r. multiflora, in the same way that the perpetual China roses are dwarf mutants of the wild climber.

Charles Marden Firch, The Complete Book of Miniature Roses. 1977, p17.

R. multiflora -- Some minatures inherit vigor and multiflowered sprays from Rosa multiflora, usually through the hybrid polyantha shrub 'Cecile Brunner' an old rose introduced in 1881. For example, miniature 'Cinderella' is 'Cecile Brunner' X 'Tom Thumb'; and 'Baby Betsy McCall' is 'Cecile Brunner' X 'Rosy Jewel'; both hybrids show multiflowered sprays characteristic of the multiflora rose species. 'Pink Clouds'. a primary hybrid of miniature 'Oakington Ruby' X R. multiflora is used at Sequoia Miniature Rosa Nursery as understock for their mini tree roses. Older books list R. multiflora as R. polyantha. An interesting strain of R. multiflora is offered as R. multiflora nana in some seed catalogues, such as Geo. W. Park Company. The seed produces charming bushy mini roses, 8 to 15 inches tall, with clusters of white to deep pink flowers, usually single but some with almost double petals.

and p57.

ROSA MULTIFLORA NANA is a dwarf strain of the common species multiflora rose so often used as a living fence. Seeds of R. multiflora nana germinate easily and soon produce bushy plants with a spring display of single to almost double fragrant flowers, white to dark pink. This is fun to grow but is inferior to modern hybrids in its ability to last and in its blooming season.

Sean McCann, Miniature Roses For Home and Garden. 1985, p69.

Finally there is another area of propagation -- growing miniatures from seed. the raising of roses from your own seeds is discussed in Chapter 10 on hybridising but frequently 'miniature rose seeds' are offered in catalogues from general nurseries. These are not really seeds from miniature roses but come from the Fairy Rose, or R. multiflora nana, and the results will be disappointing in most cases. The seeds are very fertile but the plants they produce are seldom in the miniature class (though a couple of varieties that have won prizes throughout the world were a result of these seeds). For fun, plant some of the seeds but don't expect too much. It is much better to do some hybridising yourself using the true miniature roses.

and there is more...

William Robinson, THE ENGLISH FLOWER GARDEN. Fifth Edition, June 1896. p.764.

POLYANTHA ROSES. -- These are often of a dwarf bushy habit, rarely exceeding a foot in height. The flowers are naturally very small, but delightfully fragrant. They are equally as hardy as the Tea Roses. They do well grown in pots in ordinary or unheated greenhouses, and make capital window-plants, providing they have proper attention. Rather small pots are best, and a good-sized plant may be grown in one 5 in. in diameter. A mixture of sandy loam and decayed cow-manure suits them well, and is advisable to repot in the summer, immediately after the plants have flowered. After repotting, stand them in a sunny position outdoors until the end of September, when return them to a cool airy position in a greenhouse or frame, where they may remain at rest all the winter.
    What pruning is required should be done early in spring, just previous to starting the plants into growth, and it consists in cutting the shoots back to within two or three buds of their base. Comparatively little water will be necessary during the winter, but give more in summer, and when showing bloom occasional doses of weak liquid manure. Other many flowered or Polyantha Roses are similar, or, at least, some varieties or them, and should be extensively grown in pots by amateurs.
    They are, however, hardier than the Fairy Roses, robust in growth. Besides being grown in pots they make charming masses in beds or borders, and are useful for edging Rose-beds. Some nurserymen make a speciality of these Roses, growing them as small standards in pots, and in this manner they are effective when laden with bloom. Among the best varieties are Anne Marie de Montravel, pure white, very free; Little Dot, soft pink; Mingnonette, pale rose, very pretty; Perle d'Or, nankeen-yellow; Paquette, white; Blanche Rebatel; Clothhilde Soupert; Georges Pernet; Gloire de Polyantha; Golden Fairy; Madame Allergatiere; Marie Pare; Max Singer; Souvenir d'E. Chatelaine.
    There is some danger in taking up seriously new classes of Roses of this kind, because there are very few that are not inferior in beauty to the lovely Tea and other roses that are now obtainable. Roses that have not the finest forms and are unfit for cutting for the house, are likely to take a back place, and really deserve it.

Kamila, my apologies for people not using the metric system, 1 inch = 2.54 centimetres. In my opinion, I think that the original dwarf sport of Rosa multiflora might have been white and single just like the parent. However, over the years people have been sowing open pollenated seed and this has become "contaminated" by different coloured and shaped roses. Some of the plants offered I would say are definitely hybrids: https://www.westcoastseeds.com/shop/flower-seeds/rose-seeds/garden-party-mini-rose/
In the U.K. Thompson & Morgan offer 'Garden Party' too with a picture identical to the one posted  by José Rojas in the 'Garden Party' profile. These are the seeds I sowed three years ago and from 25 seeds I had 100% germination; 25 roses for €1.14! The colours range from white to dark pink and single to semi-double and they varied in growth from a 15cm runt with tiny distorted flowers to a very pretty 0.5 metres with semi double pink flowers in the style of 'Rouletii' or 'Sweet Fairy'. This makes a very attractive little bush throwing up spray after spray of flowers right until the end of autumn. I will photograph some of the different types this summer. There was one with very dark single flowers that is darker and redder in real life than the photograph shows:
http://www.helpmefind.com/rose/pics.php?imgID=307688
and I am germinating seeds from this right now and will take cuttings. Maybe the plant that Loubert offers a very good form, it looks a beautiful flower but is not pure R. multiflora nana?

Best wishes, Andrew.

P.s All my plants flowered within 3 months of germination. I read somewhere but can not recall the reference that flower buds can be seen forming whilst the seedling is still at the cotyledon stage.