*Long explanation, then a short one... then a disclaimer...*
Cool business. Judging by the sound, I THINK Falcon autocanceled a uair, and simultaneously landed on that little lip, which is really a tiny slope. Brawl's moveset, for a lot of people, has bits of momentum shifting going on. Kirby uses that to help his recovery (fair, i think) Now, hilldashing (that's what its called, no? side-b into slope for a slide? whatever its called) is based on hitting the ground such that the attack is canceled, but momentum is not. Apparently, ACing aerials lets momentum carry through the landing, while keeping the AC lag(lessness). Ike's Aether does something similar, but since he can't autocancel it, he slides while in lag. But I'm pretty sure that Falcon fastfalled it, and the autocancel kept that momentum, like aether.
I'm guessing that the FF uair ACed on the slope, allowing for Falcon to (probably shouldnt call it this... but) Waveland, which he used to grab MK, and was undeniably awesome. (a little ways into that sentence, i realized just how much smash lingo there is... ff uair ac...)
(There's so many places i could be wrong, so it's probably not a good idea to take this as an explanation yet...)
