Part of the problem is he sounds like he was having a meltdown of some kind, and most likely he was off his face and causing a noise nuisance rather than being a threat to anyone. It shouldn't have been a matter for the police but that's who gets called. I shouldn't think they had much training for the situation they had in front of them.
My sympathy stops there because there's a procedure for subduing and arresting people that's non lethal, and that clearly wasn't followed
He was covered in blood and had his Dad by the throat saying he was going to kill him. And you don’t want to call the police?