Apparently your victims don't have to have war mode on. I didn't have war mode on and I was just killed by a same faction player and received the debuff. If I wanted to participate in that I would have turned war mode on. Feels bad.
A tip: Multiboxers are now your best friends. I just managed to get 7 very easy kills all in one go just by attacking a group of low-health multiboxing druids.