I've seen it multiple times. Its about as clear cut a yellow as you get for me. The intent was to make a cynical challenge, not to injure the dude.
Tackles like that happen all the time, I'm not sure I've ever seen a red for one before this game.
The worst bit for me was that it took 5 minutes to make a decision, even in a friendly that isn't on. And allowing one of the managers to make the dcision for him is an absolute joke, even in a friendly! I see why a red was given and I understand all of your arguments but to me it isn't violent conduct or serious foul play, so therefore not a red.