You have a pretty low view of humans if somebody simply not trained will walk around and kill every other moving human on sight, and even hunt down those trying to escape. And wear a totally nuts expression while doing it, screaming like an animal. It's more than likely the queerats never even taught the poor bastard to talk and treated it like a tool, but it should still be a fiend by the original definition, if the defition is a murderous cantus user free of the death feedback or any other inhibitions. Since their world normally doesn't possess such individuals, it would be okay to call even the "normal" homicidal cantus users of old fiends. The emperors and such we saw historical flashbacks of.
Karma demon, from what I understood, is still responsible. An unresponsible karma demon would be another fiend.