Killed in passive mode

Ive been playing and a few times ill get killed i dont really think much of it untill tonight when I launched a nuke during the event I could see one of the high lvl players had a bounty I always ignore them and go about the fight well right after the mf turns around and 2 shots everyone who did any dmg to him and then proceeded to loot all of our stuff idk what he even got lol is this a known dick move?