Fair enough & I agree with you about the ref not having the benefit of slow-mo (as I said before, when I saw it in real time it looked like a nail-on red card).
An interesting point I guess is why did he give a yellow? As you rightly say, with the benefit of hindsight, it was accidental and didn't warrant a card. But the ref at the time thought it was an elbow and therefore, in my limited knowledge of the rules, should have sent him off (albeit wrongly). Are there any budding refs out there who can explain this?