Because Tom Johnstone had a half chance to go down the touch line. The mistake was Tom then trying to offload inside. Don't think even Hull expected that penalty to be given though.

No they don't. They make decisions on infringements.

What about the decision to pass, run, kick, tackle, time waste, hold tackler, talk back, punch etc etc. That is what influences the game.
The ref only gets involved when someone forces him to make a decision.

A high tackle is what it is, a high tackle which infers it's round the head which is presumably round the head irrespective of being virtually on his knees or not, not sure why people are nit picking here, Child knows the rules and referee's the game accordingly, there's very little leeway on his part for either side, if we know that then surely all players should know it and be aware of it, had we won all this moaning would be academic, people need to get over it and move on.

Absolutely right.
Players get to know each ref's "style" and how they are likely to ref the match and they should knw by now that Child can be extremely pedantic on certain calls.
As fans, we get extremely frustrated when the calls go against our team but, the players have to take responsibility and not give him any reason to ping us.
Having said that, based purely on stats, when you see that Child is the ref, you know that our chances of winning have reduced.

Your last sentence says it all. Why is that? Child being in charge shouldn't make any difference... But it does. Go figure