When is it okay to START pvp and not be a rat?

knocked out my first raider today after about 2 weeks of playing, after I was fighting a rocketeer, he came and finished it off (it was on fire and a couple shots from blowing up)

and I thought he was just helping as I've done that a couple times. but then he started looting it. so I ran up and aimed my gun. then he ran, so I shot.

does that make me a rat for shooting him while he was looting? or is it fine because it was my work that got that loot.