She shouldn't have hit him yes but it was little more than a little flick, when he gets up she is not acting aggressively or posing any threat, and he decides to try and take and her head off. He could have just grabbed her and chucked her off the bus or if he felt that strongly about he could have closed the doors and called the police and had her arrested for assault.
You's may applaud this but when i watch it all i want to see next is someone come and stomp his head till he stops moving.