The upstairs person did not seem "pure as the driven snow"; so IMHO he gives up self defense claim as a lawful purpose. A tool from work might possibly work as lawful purpose if he did not threaten with it.

So I break your property or steal it or rape your wife or kill your dog. You're pissed. You should call the cops, but what if you came up to holler or to effect an arrest? IMHO, not a good move but it could be considered lawful after I committed crimes against you already.

NJ law has strange application, though I would like to see a better rule for them on 2A individual rights. This case does not seem like a bright point, though.