how can you say that he did a particular technique wrong?
Because he didnt do a technique at all. Not one he was authorised to use. He went rogue and body slammed her to the ground in a fit of temper.
you dont know what he was trained to do
I know what he wasnt trained to do, and that was body slam a child to the ground.
so you cant say he did this wrong
I absoloutely can. Just like his employers have said (they are the actual people who trained him btw)
that's different to acting like you're an expert on police hand to hand training.
Which isnt something i have done.
sometimes the normal techniques dont work and you need to, more or less just "do what you need to do"
He didnt try the normal technique. He needed to bring her to the ground. He didnt need to body slam her in order to do that. He needed to employ his training. He didnt.
expecting someone to religiously stick to their training with no deviation whatsover is wrong, that's now how it works in reality
Well his employers disagree with you. They expected him to stick to his training. He didnt, and the reality of that is that he is out of a job.