Sorry, Sparks, didn't read your second post clarifying that you realize one kill doesn't mean one mafia faction.
Also, I keep seeing poisoner mentioned. I hadn't heard of it until prof mentioned it as a possibility for why we might be seeing only one kill, in a post made before RCT's claim. A poisoner, according to my research on the wiki, takes the place of a traditional kill for mafia, so in a one mafia faction scenario, it wouldn't happen in addition to a regular kill unless the poisoner wasn't mafia.