to add to what I said, about the playing video games 10 hours a day, while I cant say I know why he does, I know that for many people who are not very social, or have trouble with social stuff, usually have tons of time to spend doing whatever interests them. This is true for anyone, not just people with autism.
I am not a very social person and most of my friends are people I ride with. I compete at the pro level in cycling, and am able to, not because I am exceptional in anyway, but because I dont have a job or much of a social life, so can easily devote 6 hours a day to training

He might be in the same situation of being really good at video games because he spends 10 hours playing them, with very few other things to think about