[@Rodiak] Her phrasing tipped him off, and Damien's arrival to the scene so quickly amplified the feeling of darkness in the area, allowing him to connect that a demon is nearby. 

He's simply talking to it here nothing magical, but if he still senses it, he'll put the blindfold on to try dispel it directly. If she plays her cards carefully until Damien arrives, then he may simply overlook her demon to assume that it was actually him instead.