Sounds like you handled that well.
A lot of you know I've been dealing with this at a very low level, but one thing I've become convinced of in dealing with it is that this is the level that needs to be taken a bit more seriously, in terms of prevention. I think that too often it's not addressed until behaviors have really taken root and/ or the kids involved are less willing to listen to authority figures.
I think having some sort of knowledge of how to strike back if necessary is good. My kid knows how to punch, hard, and while she never has, she knows that I am fine with self-defense, and I think that gives her a measure of confidence.
One of the things that has seemed most helpful to me is for a kid to have a wide circle of friends, so that it's easy to move on to someone else if a given kid is being obnoxious or worse. I read something somewhere (sorry, can try to track it down if need be) that small, intense groups are more susceptible to social bullying, as the bullied kids feel like they have nowhere else to go and so they put up with it. I think that parents can help with that at the earliest stages, when we're still the ones who have a lot to do with our kids' social lives. I know some parents who try to identify the "popular" kids and pursue social stuff with them, while shunning the more "unpopular" kids. (I'm talking about kindergarten/ first grade level.) The parents who were much more freeform -- if the kids got along, then they got together outside of school too -- seem to now (third grade) have kids who are more socially adept.
Freeform is huge in general, another article (dammit, same disclaimer) was talking about ... oh, playground coaches! An op-ed in the NYT. It drew a connection between the lack of unstructured playtime for kids and the rise of bullying, I think he had a point. (I think he hated on playdates too much though, they definitely can be freeform and if they're scheduled in a freeform way, too -- c'mon over, you too -- I think they serve many of the same purposes as just hanging out with neighborhood kids.)
Anyway, if kids have too much supervision early on then they don't learn enough kid-code stuff to protect themselves when supervision is no longer happening.
edit: but sometimes it's not a matter of being able to protect themselves in that way. The kids who haven't experienced negative consequences for bullying from when they were little (3rd grade say) will keep bullying and keep getting worse. They're gonna find someone to bully, and it's not always possible to keep them at bay. Too much risk of circumstances intervening in some way, just dumb luck. So parents/ teachers do need to take this stuff seriously and do what they can to prevent it.