"Not technically lying" might work on some teachers. Probably does. There are plenty who'd be happy to give kids the benefit of the doubt, fill in the blanks with what they're supposed to believe.

Unfortunately for Tim, Joel's not one of them. He keeps his eyes fixed on Tim, not threatening, but also not giving him an inch of breathing room.

"Is that what happened here? You sleepwalked right into my locked supply closet and right out again with - coincidentally - all the ingredients you'd use to make a Polyjuice Potion?"

If Tim wants to lie, fine. He can't really stop him, after all. But if he is gonna lie, Joel's gonna make damn sure he does it outright. No weaseling way with vague references to sleepwalking and hoping he'll get off the hook.