I suspect Pisgah is right, the box was an added burden (cost) that he wanted to avoid, - and as it wasn't explicitly promised in the auction, and he was already at a loss (he sold it for less than he paid, plus the additional cost of the stock-parts) he didn't want to compound the loss by sending a box he was under no obligation to send.
Had you inquired, he probably would have sent it if you paid for the postage - costs... most collectors would, as Pisgah rightly states, the box isn't worth much without its contents (rifle).
Also, it never hurts to ask on the forums if a certain rifle has a history, thousands have been recorded and you would be surprised how many have been enhanced in the last 15 years, I see it all the time, usually just swapping m/m parts with ordnance spares or maybe with more correct parts, but often enough outright frauds... If you ask here, either in a post or directly, or on Dave's "auctions" forum, both of which i go to daily, I will do a quickie search. All I ask is reciprocity, in that if you get the rifle you share its data with me or the forum...