Did I kill a player?

I’m new to this game, never even played The Division 1. From what I’ve read it looked like PVP was limited to whatever the Dark Zone is. But are you able to kill players if you’re not there? I’m level 6, I was on my way to do one of the side missions for the theater to unlock these improvised gloves, on my way there someone who I thought was just a bad luck moment for me that was highlighted yellow like a boss ran by, level 6 also. I killed them and they dropped a bunch of stuff including a level 30 weapon. Does that mean you can kill players when not in the dark zone?