Backyard Gardener's information is somewhat misleading. The statement about resistance actually applies to roses in general. If you look at the paragraph, you'll see that only the first sentence applies to Vintage Visalia. Incidentally, even that first sentence is misleading. Vintage Visalia is not a "single" rose in any sense. It's not "single" in petal count because it certainly has more than 7 petals, and it's not "single" in terms of inflorescence type because it blooms in clusters.
Here's the information Backyard Gardener offers:
'Vintage Visalia' is a Floribunda rose which produces slightly fragrant, single mid-pink flowers with the a darker shade of pink on the outer petals. In general, roses are a large group of flowering shrubs, most with showy flowers that are single-petalled to fully double petalled. Leaves are typically medium to dark green, glossy, and ovate, with finely toothed edges. Vary in size from 1/2 inch to 6 inches, five petals to more than 30, and in nearly every color. Often the flowers are very fragrant. Most varieties grow on long canes that sometimes climb. Unfortunately, this favorite plant is quite susceptible to a variety of diseases and pests, many of which can be controlled with good cultural practices.
