If he had asked her about it she'd have insisted that the tone of her smile meant nothing. Roxy was many things, but she wasn't so stupid as to tell him that she honestly couldn't care less about disinfectants and all that when they were there to dance. And Roxy's natural inclination would have been to crack a joke as well, which wouldn't have gone over all that well either.
Deep down she probably did know about formaldehyde, yet again it wasn't important to her. "That makes sense, for him," she responded, aware of the slip but certain nobody else heard him. Roxy had slipped up like that before as well, but saying 'Frigg' usually had people thinking she was frustrated and not talking about someone. Lucky, that.
Pleased to see him smiling again, Roxy continued to do her wiggling-shimmy-flaily move mostly in time to the music, surprised -- but not in a bad way -- when his hands made contact with her hips. "That's a good idea, now you can follow my lead!" And people around them were touching while they danced, so it helped them blend in as well. He was so smart, picking up on that!