He was completely out of control. It was a terrible challenge. My feeling is Madden knew that and purposely left it out of his match report to save his blushes.
You surely can't compare that McKenna tackle, a potential leg-breaker, to some Morelos petulance. Edouard went off injured, Brown got on with the game, as did Christie and Ralston after some play-acting. The ref saw all 3 incidents and decided there was very little in them. I suspect the Brown one would've been a booking, had it happened later in the game.
There's a difference between the referee seeing the incident, and you being utterly astonished if he hadn't.
From what I see, Shay Logan blocks his view.