The yellow might have been harsh. But don't look at that incident without context. That was the third/fourth/fifth high/late hit on Faf in the game, Itoje hit him twice before that happened and got penalised for both of them and George also had a late hit on him, but the ref played advantage for that incident and we scored a try, so he didn't go back for the penalty.
Mako got the yellow because his teammates infringed before him, and perhaps him feeling the effects of altitude so late in the game, caused him to have delayed reactions.
It doesn't matter what Faf did, he had the ball, he didn't infringe, he's tiny. The big guys should have known better.