I didn't check with Snopes. Is it in the "fake authorities" bag, along with Wikipedia, Amnesty International, New York Times/Washington Post, etc?
The old name for "false flag" used to be "agent provocateur" (from the French - in the more limited sense of pretending to be on the opposite side with the goal of stirring up trouble). I suspect that "false flag" is actually a coded dog whistle for "Democrat/liberal/Jewish conspiracy", and so doesn't apply to Russians - even Russians who pretend to be US citizens.
Concerning the Russian attempt to influence US elections and Mueller investigation, have patience, we haven't got to the computer hacking yet.