First, no, it doesn't. Do I wish FNA developers updated more instead of making horribly hacked branches? Of course, but I don't think I've ever had FNA stripped of its trademark and coined as something written by someone else. Even FNA itself had the sense to change its trademark once the code was too different from MonoGame's, but was still getting bundled in MonoGame's advertising as the "same" thing. And as far as the FNA "business" is concerned, I don't think I've lost clients from such a thing (even if the number seems to be dwindling a bit).
Second, as we're seeing with Unity3D, UE4, and their attached code/asset marketplaces, where the whole point is to sell somewhat similar products as proprietary packages to the people that use them, it's pretty clear that the people who would rip things off so shamelessly (and that's not even factoring in asset piracy used in commercial titles, which is also a thing that I swear exists) wouldn't have the mental capacity to steal the sort of thing I work on anyway. So in a way, I actually appear to be better off than those making these half-proprietary-half-permissively-licensed assets.
Case in point: Everything in this video.