They (not Trump of course) had to walk it back when it turned out not to be true.
Is there some outside groups posing as others, possibly, but to blame a majority of problems on them is just BS.
I see a lot of mischaracterization of what is a category, not a group. From what I can tell antifa is anti-fascism, and somewhat characterized by people willing to take direct action.
So when you say 'From what I can tell antifa is anti-fascism' - what does that mean? America doesn't have any serious fascist groups - from what I can tell the ruling powers are decidedly corporatist and the first alternative philosophy seems to be light/moderate socialism. Second is maybe libertarianism.
So who/what do you think the anti-fascists are opposing, and what would they espouse if they ever decide there are no fascists for them to define themselves against?