Well, to be fair, the captain could have said that the 'aggressor' would be handed over to security at the airport purely as a means to reassure the other passengers and to make the 'aggressor' reconsider what he was doing before things escalated.

At the end of the day the incident, while completely unacceptable, wasn't THAT serious. While personally I think he should have been handed over to security, it could be that protocol or personal judgement deemed it not necessary.