Imagine this:
Player 1, 2, 3 and 4 join a match. Player 3 drops out. Now they have the option of turning player 4 into player 3, or locking Player 4 as player 3, but now player 3 joined later.
It is within the realm of possibility.
Faking a video is incredibly hard to do. Also, the select screen is heavily based off of the new leak, so they would have had to fake this video within around 24 hours. The camera isn't 100% shaky, so if you want to prove this fake, try to find a point where sonic doesn't move with the rest of the screen naturally, as that would have to be done by hand.
We have no idea what his situation is, and hence I would argue it's impossible to determine what he could and couldn't do. Also, for all we know he LOVES Metal Sonic and this is what excited him most, and he wanted to share.