I think the thing that saved Nunez was that, being Darwin, his kick mostly missed its target.
I think we’ve seen reds given for less, and while I agree it was a yellow, I can also see how some refs might have given a red.
I think that when you look at it again he barely connects, no excessive force and no studs. It’s wreckless, off the ball and a blatant yellow. But I don’t think anyone gives a red there.