Skip to 3:42 of the above video. That, according to Past to Present Online, is a build of Killer Instinct on the Xbox 360.
Double Helix games created the reboot of the fighting game landmark for Xbox One, but here we're looking at an alpha that, Past to Present Online tells Shoryuken, is beyond some proof-of-concept or pitch stage. In other words, this was made after they got the job from Microsoft.
Still, it's not entirely complete, with some textures missing and other assets incomplete. PtoP says the footage comes from "slightly before the game's cancellation on Xbox 360." Only a few levels are playable without crashing the game, and only three characters are present.
Still don't believe the video? Go to 8:55. A completely gray character model of Thunder shows up.
What does all this prove? Other than some form of this was playable on the Xbox 360, only that at one point it was being built for that console until Microsoft likely realized the title's value to the launch of Xbox One last November. It doesn't mean Killer Instinct was meant to, or ever will, come to the Xbox 360.