> No one claims NFT proves ownership of entities outside of the used blockchain. But within the chosen blockchain, they do prove ownership of that particular NFT. That's a fact.

I think the author's underlying point is: what is the value in having proof of ownership on a blockchain if it does not correlate to real world ownership in any meaningful sense? The cited example makes this clear: if you steal someone else's art, turn it to an NFT, and then sell it to a third person, the buyer does not actually own the underlying rights to the artwork because you never had the right to sell it in the first place.