I don't want to play with words here...multiple things can be true at the same time.

True, but your Reuters quote affirmatively stated that Antifa wasn't an organization, but instead was a movement. It didn't say Antifa was an organization. It doesn't support your point. You might disagree with Reuters characterization of Antifa as not an organization, and claim that Antifa is both - but the Reuters quote doesn't say that.

Again, because Antifa isn't an organization. There's no "leader" of Antifa. There's no structure. It's just a system of beliefs and tactics that a number of people subscribe to. There are organizations of people that ascribe to Antifa beliefs and tactics, to be sure. But there's no national organization that directs or controls or guides all these folks. Unsurprisingly for any system of beliefs based on a published guide of principles and tactics - and where people can all find and talk to each other on the internet - many of these groups will say and do many of the same things. Which doesn't mean they're all part of one large organization.