I do believe him when he said that Kareem won the starting job. But I'm sure he would've liked Hayes to take 40%+ of the snaps and be an anchor against the run; I doubt he's excited by Ade Ogundeji having to now take 20 to 30 snaps a game.
Hayes will likely be a rotation player at Oklahoma, too - it's not like he transferred to a low-D1 school where he could be the unquestioned starter. He would've likely been willing to stay as a rotation player at ND, too, if Shanty weren't such a fucking dick about pretty much everything he does in life.
The conversation they most likely had about his future is one that could've been very different if Kelly had learned (somewhere along the line) to be humble, self-critical, constructive or conciliatory in his approach. At this point, the ship has sailed on that front - he's a dick for a life, it would seem.