Killing people is not considered griefing in any full-loot, open-PvP mmorpg. Just look at EVE Online. I'd say that griefing is stalking and repeatedly killing a single person for no apparent reason. If I spent an entire day bombing some dude in NCR and insulting him before replication kicks in, yeah, I'd be griefing him. If I met him in the wasteland and gunned him down, well - that's just a FOnline way of saying "hello, how are you today?"
Random violence in unprotected locations and random encounters doesn't mean somebody doesn't like you and wants you to feel bad, it's just the way this game is. Most people shoot unknown characters because they don't want to risk getting killed, they want to obtain loot or they want to deny information to their enemies. It's nothing personal, really.