That was pretty god damn amazing right there. Yes, time sped up in a couple of places. No, he wasn't using the ~ key because that would have made it too fast for him to control anything; maybe it was a bind he created to speed up the game by 50% or whatever. Either way, as Majin You said, the fact that you can speed up the clock doesn't make it any easier for you to stay suspended off of the ground until you get 45 1 ups and come down without taking any hits; if anything it makes it actually harder for you to control Mario and requires you to react more quickly to what's going on.
Mad skills right there, although it does seem like an awful huge waste of time for any reasonable individual. Still, I wouldn't call that guy out on it, obviously that's what he's good at. I wouldn't be surprised if he has a job testing video games, or if he'll end up getting one.