I think to have the confidence at an individual sport like Tennis you need to have some arrogance as whether you win or lose comes down entirely on your shoulders, and his moodiness on court is because he is so focused on winning. As for the interview, maybe he is shy or doesn't like interviews, he is a sportsman after all, not an actor. At the end of the day it has nothing to do with what a fantastic tennis player he is.
I will definetly be watching him play Nadal and win or lose I will still be cheering him on!
