You are assuming he made the right move. Judging from how I've reacted in violent situations, I'm pretty sure I'd go in if it would help. Always have before even when weapons were involved - wasn't always the smartest thing to do is the point though. That guy had a gun. I would have been scared shitless to throw myself in harm's way, only to find that somebody else accidentally got hurt or shot or killed. That would be the only thing holding me back. It's only fucking money. Now, if this guy had killed before and I KNEW that, I'd probably be more likely to take the risk and do something to prevent him from doing so again.
The guy is definitely a hero but judging from the way he was talking, I got the impression he did it for selfish reasons and wasn't really all that concerned about the other people in the bank. I'm not saying that was the case, I'm simply saying that is how he came across.