Except it was the guys posting game screenshots that leaked that. Not the guide guy. The guide guy leaked like 10 pokemons at most, and some too blurry to be properly visible, and yet since he's the only one that maybe signed NDAs he's the only one being investigated.
Don't try to fool yourself this is about "w-we pwned TPCI and the game is proved SHIT!!", this is strictly about them wanting to stomp down an internal leak. Literally internal, since the guide is apparently published by TPCI themselves, so chances are it was one of their own employees.