Bug? Ossecati, Boneshaper spawning Prophecy mobs instead of skeletons

I encountered Ossecati, Boneshaper in a corrupted zone and he was possessed by a Tormented Warlord (I think). He kept spawning purple zombies instead of skeletons like he normally does. There was no prophecy active in the area, or completed despite a full-clear of the area.

I couldn't find a corpse-targeting skill so I didn't get the names of the spawned mobs.