For the moment, he's too focused on the game to notice he's not actually alone in the room anymore. He's making a decent run of it and improving on his paddle timing even though he knows he's not where he's going to need to be yet. It's a start, at least.

When he finally loses his last ball, he huffs out a breath and starts to take a step back before he gets the sense of someone else being there, so he halts and turns in place instead.

"Oh! Lan Wangji!" For multiple reasons, the urge to laugh comes upon him for a moment, but he manages to channel it into a bright grin for the time being. "Hello! How long have you been here?"