That's not the case here at all.
In your case you'd be covered.
In the story the op states the homeowner has already been told the police are on the way. That's the big issue here.
The alarm company asked and the HO approved the police dispatch. He should have waited for the police.
Had he shot the people knowing that police were en route he'd be on the fast track to prison.
You can't knowingly inject yourself into a situation where deadly force is authorized. Especially if you know the police are on the way.
Sent from my teepee using smoke signals.