The original chinese leak says that "Logo diamonds cause Pokemon to transform shape, like Ash-Greninja". He is only offering and example of transform shape, not confirming that Ash-Greninja is into the games.

Here you have the original message:
http://www.smogon.com/forums/threads/gen-vii-pok%C3%A9mon-sun-and-moon-new-info-post-5834.3549746/page-199#post-6888716

Also, stop from saying that "the real leaks" are fake because Arcanine is in normal form into the games. That was a different post from the original poster and we don't have clues that they are the same person.