Help me figure this one out:

I was riding behind a guy on a MTB and when he would stand up to pedal the tip of his seat was about level with his waistband. He would stand up straight as a rod when he pedaled and the whole thing just looked strange. Going from standing to sitting he almost had to leap back up to be seated. When seated it did look like his legs were extended on the down stoke a little too much.

When I'm standing the point of my seat is level with the bottom of my back pocket.

Anyway, was the bike just too big for him or was it simply a matter of a seat being positioned too high?