Re: Hostage situations...
"In this case the police merely acted as a proxy - so the person who originally did the swatting is guilty of "pulling the trigger by proxy". (If such a term do exist in law)."
No, he's not. He's guilty of lots of offences, but he isn't in control of the police. He's relying on bad training to get the guy killed. Actually, he's not even doing that : if he wanted to get his friend killed, he'd have given them HIS address. We have to assume he was trying to frighten his friend by calling the cops for real, not by having some killed for real. Either way, he probably isn't actually guilty of anything more serious than wasting police time, misinformation, putting the victim in harm's way etc. The policeman pulled the trigger, and he did it in contradiction of his training.
As to whether the policeman should react like that for his own protection : in a dark alley, without a clear view of the assumed shooter, with no backup : yes, it might be a reasonable reaction.
He's been called out, with support, to an incident with no verified report of a problem and shoots a person who is outside their house and has got there without preparation, carrying nothing visible and until recently having his hands up. It's likely he drops them slowly, tiredly, unconvinced he is at risk. Not in a way that appears to be diving for a concealed weapon.
The likelihood is that the victim can, at worst, bring out a heavy handgun and fire it quickly without the opportunity to aim it. In comparison, the policeman has, if he's working to training, got a rifle with which he can make an accurate shot over a range the victim can't match, he has cover behind his cruiser, and has colleagues also able to shoot if sufficient threat exists. If the victim brings up a handgun, he's almost certainly not going to kill the policeman.
What we have here is a situation created by the actions of the telephone caller and for which they should be locked away. But the actions of the policeman are those of an untrained, poorly prepared trigger-happy fool who panics when there is a small change to the situation. This is not what police gun training is for.
And yes, a lot like the Menezes case : innocent victim, misinformation, poor police training leading to frightened officers, panic reactions and trigger-happy result . Except that in that case it was not even a situation created by a criminally stupid perpetrator. In that case, it was the police that also generated the initial situation. The only saving point is that they had prepared themselves for a bomb threat rather than a lone gunman, so the reaction of killing on movement has some limited sense behind it.
I say limited because you can't necessarily stop a suicide bomber by shooting him : there is equally good chance that killing him will permit his explosives to detonate, so the risk to the police or bystanders isn't reduced by shooting. Shootiung does not improve your chances of survival against a bomb blast. Again, poor training, bad thinking, fear, leading to panic reactions.