There are so many different kinds of sunflowers. Some have many branches and many flowers on each stem.

Hi there,
there are modern cultivars that are bred to produce multiple stems, for cut flowers. (The single-flower ones are used for oil/ bird seeds.)
----
The center/ top one tends to be the largest. But with some decent feeding, those buds will come along nicely. Some seasons ago, the communal gardeners planted a great annual display including pale multi stemmed sunflowers. Plus they definitely got the fertilizer right. Those specimen were a show to look at, and those side buds grew on quite long stems, more than a dozen per plant.
----
so, no, probably not diseased, just more fun when cutting a bouquet.

have a nice summer, bye, Lin

I saved some Mammoth seed from last year. Here's one result.
{{gwi:22612}}