I think if the bench would have stayed where they were when they first stood up, they probably wouldn't have been ejected. They were on the court, but not much, and there was a gap between the action and the players. However, when it started to escalate, they ALL came onto the court, inside the 3-point arc. That's why they were ejected. The problem is that the more bodies that are present, the more likely it is to escalate. If everyone stays away, the refs can control the 2-3 people involved. When it gets crowded, more chance for a brawl. Refs were correct for removing the entire bench.
I didn't see it (too lazy to look) so I'll rely on your and others' assessments of the ejection/aftermath.
My issue is it being allowed to escalate to the point where a fight could happen. Did the refs not issue T's earlier when it was clear that level of talk was happening?
I'm leaning to blame the refs on this one. This should never get to this point.