I don't think it's a scam, personally. I think the buyer expected to have the camera in-hand today, thought that's what he was buying, and when the camera didn't show up this morning he filed a claim as if you had advertised guaranteed delivery by 5/2 A.M..
Either that, or the buyer bought more than one camera hoping to get it by date x, and planned on shafting the seller of whichever camera arrived 2nd. Try doing an Advanced Search on everything he's bid on in the last couple of weeks. Look for another camera in the results. Years ago I had a bidder do this to me - he had bought three identical items over two weeks for varying amounts(one of them from me, for substantially higher than the others), and filed a claim that mine was of poorer quality than advertised/pictured. I was able to point to the other auctions and descriptions and show what he was trying to do.
I had that thought as well. What if the guy needed a camera for this weekend.
He paid yesterday, and maybe he thought 2nd day would be today, or maybe he didn’t realise FedEx wouldn’t ship saturday. 5/31 may have been too late if he needed the camera for Memorial day.
He might not have realised that before he spoke with you.
So it might not have been a scam.