First off - this may be the first uncaught fall, but it certainly won't be the last! Cut yourself some slack - it IS part of growing up. (Especially for boys.) =)
That said, if he's not complaining, I would personally be comfortable taking a wait and see approach. X-rays seem benign, but it IS gamma irradiation, and you don't want to get any of that if you don't have to. The younger, the more susceptible to the effects. And, the cost in time and money isn't small either.
I would try to locate the source of his pain. Does it hurt when you push on it? Or only when you move it? Or only when HE moves it? Is it painful in one specific spot (called "point tenderness")? With point tenderness, I would probably put in a CALL to the clinic for advice. Otherwise it's quite safe to wait a few days and see if it passes.
However, if you're nervous, give the clinic a call. It seems the doc is comfortable telling you to wait it out, so it doesn't hurt to ask again if it gives you peace of mind. =)