Yes, that is indeed the Pyro that you see there. In the video, he gets to race against a pack of videogame celebs. And then transform into a heavy on a motorboat.
We're not exactly sure where this has come from. The Youtube comments suggest the characters are hidden, but accessible via mods, on console copies of the game with reviewers right now.
If so: exciting!
Thanks to Mr Tony Heugh for bringing this to our attention.