That piano player in the video is hardly what I'd call a savant, more like he hit his head and woke up as a douchebag but music is one of those things that gets stored way back in your brain somewhere, I think. I have songs stuck in my head all the time and I'll sleep for 12 hours and the damn thing will still be there. Maybe after a head injury some people can recall tunes they've heard throughout their lives more clearly which would make them easier to play.