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?
Corporatism was inseparable from fascism in Italy and Germany. The exploitation of the profit motive is one of the primary reasons that so many people overlooked the atrocities.
Fascism is the reason so many companies like IBM, Hugo Boss, L'Oreal, Koch Industries, Audi, Porsche, Adidas, BMW, and countless other extant corporations have dark histories from supporting the German extermination camps to utilizing their slave labor to build their products.