He doesn't even seem bothered by the sudden interruption. The only indication that he's noticed anything at all is the slight glance in the boy's direction. He doesn't acknowledge him any further, though, until he finishes reading what he was in the middle of.
Once he's done, he sets the paper aside and looks up at the young man sitting across from him. He gives him a moment or two to say something, but when he doesn't, he prompts him. "What can I help you with?"