Puzzle games are quite time consuming titles. They require logical and lateral thinking, timing, finesse. You have to sit and think for a while about each solution, but perhaps if you didn't the game's wouldn't take that long at all. We've seen that in Portal runs before, so it wouldn't be surprising if the same was true for games like The Witness.
In-fact that's exactly what's happened with the new Jonathan Blow built game. Despite it being claimed before release that the game had around 100 hours worth of puzzles and secrets for people to work their way through and find. One speedrunner has managed to do it all in just 25 minutes.
Of course the above video contains just about every spoiler possible in the game, so don't sit through all 25 minutes and then realise you've just ruined the game for yourself. But if you have already beaten it, something tells me Azorae there has managed to do it faster than you can.
It's perhaps more impressive in a game like this than in a shooter or platformer, as there are a lot of puzzles in The Witness and all of them require precise movements and selections. Azorae memorised all of them, their solutions and the quickest patterns of movement to complete them in.
That's quite a task. Boring if you prefer the idea of games as fun asides, but for those that like a challenge, this is an amazing feat.