The thing is though, it's just a theory, so you don't have to believe it/ take it in if you don't want to. Mat doesn't want to force you to believe in his theories, he just wants to create interesting video game theories that could be canon.

Like it was actually Cloud that killed Aeris, Sephiroth only paralyzed her, but Cloud by drowning her, killed her.

Or Link is dead during Majora's Mask

Or even the theory that Mario is a sociopath.