. . . when going for the ball, and very few of them manage to keep the ball in-bounds, which means that play continues and your team is down a man until you get back on your feet.

I think he was pushing off trying to get back onto the court, but he underestimated how much his momentum knocked the coach away, so he got no stability from the push, and the push looked way worse. After he lands, it's pretty clear to me he expects to regain his feet and run back out right away, but his momentum keeps going backward. Is that a jerk move, particularly with no concern for the coach you bulldozed? Maybe. I don't think it had anything to do with frustration with the game, though. No one lashes out at opposing assistant coaches who are buried in the middle of the bench when their team is losing.