I couldn't tell you if they specifically said they were at the event. But they were part of another communist group that showed up to support Antifa. I can't remember the name of the group because I read about it right after the event happened. I also found out that there were several other pro-communist groups terrorizing the nation along with Antifa.
Antifa, despite what some of them might have said, were NOT their to support BLM. For the most part BLM peacefully protested. Not all of BLM and especially not at first. When the protests first started they typically ended up in riots but then calmed down. Antifa, et. al. never showed up to protest. They showed up to destroy capitalism. That is their entire raison d'etre.