I have not delivered to a B&N in years, but if I had to guess, I would bet a driver rang the bell and started unloading, rang the bell again, kept on unloading. Went around to the front and asked if someone could go back and open the door. Clerk said, "No, the receiving guy called in sick." Our guy said, "eff it" and left the pile.
I did have the almost same thing happen one time. I told them that everything was unloaded and if I had to put it back in the truck, it was all going to be sent back to the shipper marked, "refused." By the time I got to the back door, it had magically opened and there was magically someone there to accept them.
Back when I ran the route that delivered to the B&N, they always seemed surprised to see the huge amount of deliveries. It was like they thought their inventory was placed by elves in the middle of the night. Even though they got almost all their deliveries at about the same time, they NEVER had anyone in back, we regularly had to walk around to the front to get someone to unlock the back door.
edited to add. If I were presented with a photo like that to sign, I would also add: Manager at B&N agrees that there will be a receiver at the door within 2 minutes of ringing, failure to do so will be construed as a refusal and items will be returned to shipper. Hand it back and make them sign it too.