It's all about audience perception. He's never going to fully revert back to The Rock persona, because he's trying to use his return to wrestling as a springboard to where he was before he made the move into kiddie flicks: he did The Tooth Fairy and Escape to Witch Mountain and both underperformed. I guess after that he waited out his contract with Disney.
He has still done better than Stone Cold or John Cena, so he's back in WWE to re-generate the kind of buzz he had when he first left. The fact that he is not the old Rock indicates that he's not back to stay permanently, even if he says he is.