The ref gets to to see full speed, slowed down and freeze frame. He also knows the rules better than most fans. A good example of that is when Spurs had their goal disallowed in midweek. Most players, pundits and fans thought you can't be offside if the ball is played backwards, when there's no such rule. ( It's just that 99 times of out 100, when you pass the ball backwards there isn't anyone else in an offside position interfering with play.)
And then there are the rules that rarely, if ever, come into play. Did you know, for example, if a red card offence is committed and the offender can't be identified then the red card is given to the "senior team official in the technical area"?
For red card offences, the law is pretty vague. The relevant wording is "A tackle or challenge that endangers the safety of an opponent" - the other part of that law is " or uses excessive force or brutality must be sanctioned as serious foul play" which I think we can rule out in this case.
So the ref has a lot of latitude here. I'd likely have been upset if our player saw red for that, but given incidents like Mugabi's red against Hibs in the cup, it's no surprise to me when they happen.