I'm pretty unconvinced by the piano savant thing. I can believe that a head injury might somehow open a pathway that makes it easy to translate the idea of sound in the mind into the geometric patterns that it corresponds to on a piano. It's true, that is difficult for most musicians. But there are plenty of recordings out there of this guy playing and his playing is.. not that great to be honest. I've known various people in my life who developed their own "outsider art" style of playing piano just by sitting at the instrument and improvising in an informal way. It's not that rare or that difficult.

What takes practice and training is developing the physical technique to handle virtuosic works, or an encyclopedic knowledge of harmony, chords and voicings, the sort of thing that high level jazz improv artists do. In one of the interviews this piano guy talks about how after his injury "it was like the soul of Beethoven jumped into my body and took control," except the thing is, he isn't playing Beethoven. I think it would be pretty revealing to see him make an attempt at one of Beethoven's piano sonatas.