Yes, I think the seller is confusing the lid of the box (which has a label) with the slipcase. I agree with the consensus so far; AFAIK the book came only in a box, with, as Trotter notes, a tissue guard (sadly mine doesn't have this, but as it cost me only a tenner in a remainder shop many years ago, I'm not complaining).

I wonder whether this slipcase might be one that a previous owner had made privately?