It was leaked like 1-2 months ago in the XBL news thread. It had a generic boxart with only the title of the game back then. If it's an April fool joke, it must means it's also playable since the achievements are also on the XBL network.
They could have simply submitted it early cause, apparently, the submission process takes awhile.
It looks a lot like an april fools joke -- nothing about it makes it seem like a video game. The presentation is extremely unique, if it actually is a game.
The fact that there are lots of "Recommendations" from various made up establishments, and/or real establishments, also suggests it's highly unlikely it's actually a game. It's just extremely unlikely that a big game studio like Ubisoft uses that in the PR/advertisement for a game, even if it's supposed to be a joke.
If it's a real game, there's money on the line. Would a big company like Ubisoft really risk advertising a game like this?
Also, the trailer/website didn't go up until today. Doesn't matter when it appeared on Xbox Live I think, since they might have submitted it early to make sure it was up by the time they wanted it up.