She gives him a deathly serious look to disguise the fact that yes, she was worried, and no, she doesn't want to make a big deal about it because that would be admitting that she already cares about him, and she's not sure she's ready to actually care about someone again.

She heads back to the table and grabs her glass, so she has something to focus on besides him.

"I, uh, don't have a boyfriend." As much as she knows it would be a bad idea to let this get beyond friendship, it's suddenly important to make sure he knows she's single, even if he is really obviously fishing for that information.