For a mistake he was willing to apologize for on the air, I don’t think this should have gotten to the point of firing. An ass chewing, sure, and a note in his personnel file that would count against his next raise/promotion, but firing? That seems a little too far. He should have paid more attention to the music he was playing, but I don’t think this should be a firing offense.
This does, of course, assume that the guys disciplinary record is otherwise clean. While I wouldn’t fire someone over this alone, I could certainly see it being a last straw that leads to firing after a history of misconduct and/or incompetence.