The chart leak was posted in a thread on /v/ that an Anonymous user asked: "Who's getting cut, /v/?"
This was the image that Anonymous (OP) posted in his thread.
He doesn't know anything, he just posted who he personally thought was getting cut by graying out certain characters.
3 hours later, someone took the Original Posters image and modified it with the
unleaked at the time, Character Select Screen Icons.
As you can see, they are the same image, just modified with the addition of X's and CSS icons, as you can see Ganondorf, Falco and so on are still grayed out behind the icons.
This CSS icon leaker did nothing more than cross out the icons of characters he was supposedly sure are 100% cut, and then added all the icons of unconfirmed veterans/newcomers from the image he had. He seemed uncertain whether Mewtwo was in or not, so a "?" was placed. He had no image sources of Mewtwo, so he couldn't really post anything of the sort, but apparently knew something.
Only reason I see this was done is because he just grabbed OP's image and modified it, and it happened to have Mewtwo on it. If someone like Chorus Men or Dixie or whoever the hell are in the game, he clearly did not have any source materials containing imagery of them to use. So there was no reason for them to include a random google image of them with "?" on it.