Draco was probably more attuned to the slight fear in the air, and seeing the scars on the castle he'd helped make. And apparently the Weasley Twins' Swamp had either been moved or removed, but it was easy to get lost in memories. "I think what I want to find is old and lost books." It was an answer that served multiple purposes from the obvious (he wanted them) to something Hermione would like to something Hogwarts would like. And he doubted Hogwarts would disapprove of the scheming element.