It sounds like sight reading through them for the first time at tempo
That's highly improbable but if it's the case then he's a sight-reading genius, I mean all of these extremely difficult pieces? at that speed? Try to sight-read Alkan's "Le Preux" or Rach's "Little Red Riding Hood" just for fun. He hasn't got any sheets in front of him in most of his vids. Anyway even the slowest parts are completely off. I'd imagine if he has such good reading abilities he'd get some of it right? He hasn't posted anything serious, on that channel at least. I don't know what to think really
However there is also a probability that this is as good as he can get
He does state on his page that he posts things once he has "learnt" them.