Puck interrupts Fabled Elder Eoten boss fight

While fighting the Fabled Elder Eoten solo in a Watch (i.e. multiplayer) vault, Puck appears. I spoke with him after defeating the boss and his monologue was about killing a Carnute for the first time, but I've never killed one (I don't even know how (I know with some sort of spell but not which one)). Not sure what triggered this nor whether it can be reproduced. Difficult to play while distracted especially in a scenario whereby I couldn't be revived (no other players or recruit).