Your dorm was next to his, it was the middle of the night and he had woken up from a nightmare. In his panicked state his quirk somewhat activated, frost covering the room (Elsa style) He was scratching at the scar over his eye, trembling as the memory of his mother burning him kept replaying over and over in his mind.

Some of the ice had been cold enough to frost your wall, even going in the hallway a bit.