I was a cheerleader and we had to do push ups at practice.. I became pretty good at them (personally thought I was one on of the best at them b/c i thought I was pretty flat rather than like a 'v' with my butt in the air)... granted if you woulda asked me to do a pull up and you woulda been outta luck <img src="i/expressions/face-icon-small-wink.gif" border="0"> like piper said, I sucked at the pull up/chin up, so i just did the timed stay where you are thing haha which is really the bicep still rather than the tricep...
Just takes time to build up, I imagine its just b/c he hasnt been using his upper body as much as his lower body. And most people have piss-poor triceps the way i understand it.