The story is that when he got the Bama offer, he didn't want to disrespect UM and leave, so he went to talk with Jimmy Johnson. JJ told him that if he wanted to be a great coach, he needed to learn from a great coach. So it wasnt as simple as Cristobal leaving UM because it was a ****show. He left because he had been fired from FIU and he wanted to learn how to become a better coach, and one of the GOAT UM HCs recommended he take up Sabans offer.
If you want to say Mario is disloyal, then you also need to say Jimmy Johnson is disloyal. I doubt most people would do the latter.