Yeah, he's not buying it. Nico knows what trauma looks like, okay, and maybe he doesn't know what the root of this is, but Tim was spooked when Nico showed up. And it wasn't because of Nico.

"I'm in 10th grade, but they put me in the 9th grade English class, so you'd have at least one person you knew in one class." Probably not enough to get through the day, if it's that bad. "Why didn't you get your guardian to call you out sick?"