The signature looks authentic to me, really consistent with other autos from Hill I've seen and it does look like the Century version. But certainly never heard of a Grant Hill buyback auto before, and I don't think this is one althought it may be a production error or sorts?
Scan of my card next to the one from the auction. It just looks very consistent, signature wise and IMO is legit. As mentioned by ducky, perhaps this was just a version that wasn't numbered from the auctions, but its still very rare and very much legit.
I know fleer did have some signed ones in stock that were sold at the auctions. How would you rub it off? Either way, I understand now why it aint a 1/1!