With the amount of time left, the only option was shoot a jumper.
If you're playing someone for a drive, you backoff and give them a shot. The Hawks hedged and played him for the jumpshot. Hence not getting a shot off.
If it was a smaller person, I have no problem with Rondo taking that shot. I've seen him hit buzzer beaters before. And if you can see my reply from during the game, his shot when he doesn't think about it looks good all of the time.