White nationalist group posing as antifa called for violence on Twitter
Blaming the boogy man of White Nationalists, Russia, or outside outside agitators is a way to shift blame by politicians and an easy scapegoat. 
Amusingly the governor of Minnesota, and a big city MN mayor blamed vandalism & lootingrioters as being the work of people who were all from out of state, thereby parroting Trump's same line (or he theirs).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.