She takes the statement at face value, assuming that Cas must know the 'man'. Does anyone even know what he is? That.. That thing inside of him!? But Cas' expression when she tells him nudges her to believe that maybe, like Dean, Cas does.

"...he's... he's a terrible person. Or whatever he is." She tugs the scarf back up, hiding away the damage, looking down at the ground while her fists clench at her sides. "He was so angry and I didn't do anything to him!"