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.
Scapegoating allows politicians to avoid angering their own constituents, and it also makes it rhetorically easier for politicians to avoid taking the demands seriously.
And a significant fraction (1/6 to 1/3) of arrests have been from out of state. So, the original claims had an element of truth.
But I disagree with you that it’s just “BS”, which would imply a level of cynicism which may exists, but for which you provided no evidence.
[1] https://scholars-stage.blogspot.com/2020/05/on-days-of-disor...