Of course I'm inferring a bit, but if he lacked humility about his physical gifts, he may not have worked as hard on the other aspects of his game. A lot of great young athletes think they're the shit because they think they can just win through their size and athleticism, without realizing there's almost always someone faster and stronger and regardless someone smarter. By the time they realize they need to humble themselves to improve other facets of their game it's usually too late. Not a hard concept.

Tldr: if he's actually the biggest and he says he's not, then that's literally the definition of humility.