Im pretty sure they could have just handcuffed him and taken him away in that case. The conveniently camera-blocking humvee and the fact that this happened so fast kinda tell me this isn't your everyday arrest. Just gonna quote a tweet from the article
Okay, so he was arrested quickly. That's still an arrest.
You don't have to be read your rights to be arrested, by the way, that's one of the stupidest and biggest myths about the legal system and it will never fail to make me laugh.
Tear gas canisters do not create sparks.