He is certainly very startled when Crowley falls into a coughing fit, as well as very confused. They are extremely good at this.

"My dear boy, what--" Oh, this is terrible. He fills Crowley's glass back up, handing it to him in hopes of helping, and glances over towards the center of the room again. There's a few people staring, but most of them seem more preoccupied with their own dinner and don't give it a second thought.

He's not sure where the person went. Takes him a second to remember that mortals use bathrooms, so he really hopes that might be the case.