It's the same guy, if you go
to Bulbapedia's thread the Chinese leaker who first got posted mentioned through Cresselia stated that Ash-Greninja changed forms through the crystals, which turned out to be wrong. He also mentioned a couple other things that were dubious and questionable like the ride Pokémon bit.
The one you're probably thinking of (the Riddler) didn't mention anything about Z-Crystal forms, but even so the first being off proves that the leaks don't have to be 100% correct.
Wasn't there speculation that he sprinkled some false info into his leaks so that he could pass them off as just good guesses if he ever ran into trouble with Nintendo? Not sure how credible/logical that idea is but it was floated around once the the errors in his leaks became apparent.
Also I find it spectacular how...enduring... some people are with their hopes/wishes/expectations for new Alolan forms:
One month to release, with 3 new Ultra Beasts and alternate forms for Necrozma and Lycanroc revealed, but new Alolan forms not even hinted at: There could still be new Alolan forms!
A fortnight to release, with the current "big news" being...Pokemon that are slightly bigger than usual (woooo -_-) and the return of the past villains for some sort of quest/storyline, but no hint at new Alolan Forms: There could still be new Alolan Forms!!!
Predictions:
The thing gets datamined, no traces of new Alolan forms are found: There could still be new Alolan Formz!1!!1
They have played through the entire game, including the post-game, filled the Pokedex and explored every little corner of USUM Alola, without discovering a single new Alolan form: There could still be new Alolo Fromz!!!2!11!
People are of course free to tell themselves that "GF wants to keep the new, amazing Alola forms a surprise" but evidence form past pre-release periods doesn't really back that mindset up. They'd at least reveal a couple for marketing purposes.
Now nothing, absolutely nothing, Pokemon-related would make me happier than being wrong about this, but it doesn't look very good right now.