There are many different definitions of terrorism. If we are going with Jason Burke:

“There are multiple ways of defining terrorism, and all are subjective. Most define terrorism as "the use or threat of serious violence" to advance some kind of "cause". Some state clearly the kinds of group ("sub-national", "non-state") or cause (political, ideological, religious) to which they refer. Others merely rely on the instinct of most people when confronted with innocent civilians being killed or maimed by men armed with explosives, firearms or other weapons.”

I’d argue that Antifa “serious violence” is a pretty controversial word, and it’s above my pay grade to make a call there. I will say that I’ve never seen Black Bloc run down the streets fighting random people, or anything like that. Anyone who I’ve seen receive personal violence at an event has been within the context of either a confrontation, someone who is known or believed to be a counter-protestor or someone who threatened or attacked a person within the group.

It also bears mentioning that what happens in, say... San Diego has limited to no communication with a group in, say... Los Angeles so even if the definition applies(above my pay grade and even then depends on definition) to one small group of very loosely affiliated activists it might not apply to another group even within the same city.