For the amount of panic that rushes through her at the start of the transformation, her expression is unchanged beyond a slight flinch. By the time he's speaking, she's settled entirely. She briefly considers whether it's possible for a drinking utensil to cultivate to human form. Maybe, there are enough stories about spiritual tools doing it... but it's much more likely that this is a guy who can make himself look like other things.

"How'd you--"

No, wait, more importantly, why? She looks him in the eye, then down at the phone, unsure which to address. The human wins out. "Why a cup?"