Ok, I just watched it all the way through. I wanna say 3 things.
1. 480i
2. Identical modeling as the Halo2 level. *identical*
3. Identical textures on the level.
I'm willing to say with quite certanity that this is NOT legit. As watching it at full 480i, I can tell by watching it. It is not running the same engine as the Halo3 Alpha.
PSN ID: Kwaad
I fly this flag in victory!