I think they mean you keep the URL and the content stays in the Internet Archive.

But it could also mean that the Internet Archive creates a special page, say, "Owned URLs", where they list a username owner for each URL that someone has payed for. If you wanted to trade your URL, the IA would get a small cut to modify the contents of that page with the new owner.

This is 1:1 equivalent to the proposed scheme, but cuts out the inefficient "mint NFT on Ethereum blockchain" step, replacing it with a simple database on the IA side.