i wasnt aware you did anything wrong.

NPC, in any RP means a character that is not playable by one player. Some GMs will say that "their NPCs" can only be played by them, but then, by definition, that's not an NPC. its a Playable Character. The guards are ok to kill, if we're going by typical RPG logic.

Then again there are plenty of people on this site who define things differently...