Probably a guide account. Happens alot. People get there accounts given guide/GM powers fo certain reasons , and SoE forget to take them away. Its not that its a full GM/Guide account , its just flagged as one , and MQ2 picks up on it
just FYI, dont trust it, I don't. I've had GM's right next to me talking to them and it not even pick them up, they can watch the zone without being in the zone, it has false positives.
I've had a slightly different issue, where on my hud I can see someone by name, and when I target them they have buffs, etc, but they don't show up on the /who list or trigger my gm alarm on the hud. Anyone have an idea what that's all about?