I can't believe people are still skeptical. I skipped around in the video to not spoil much. If this were all pre-rendered don't you think they'd choose a smoother running animation or better AI and collision detection with the boars. There's quite a bit of jankiness in this footage that wasn't present in the old, presumably faked, reveal trailer. At one point a baby boar even glitches out on a rising platform. Why would you fake something and include such obvious flaws?
This was someone playing the game, no 'canned' footage or staged scripts. The player sat down with a controller and made decisions on where to go, what and who to interact with and figured out puzzles on their own.