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.
I consider an organization on their tenets, under which Black Lives Matter is completely fine.
KKK for example isn't.
Right-wing terrorism has no redeeming kernel of decency, nor does it have a productive movement behind the (few?) bad actors.