The term for this in the general case is Greater Fool Theory - https://en.wikipedia.org/wiki/Greater_fool_theory
My question to him was, "Would you buy the ownership of Heroes by David Bowie (his favorite song of all time), for $2000 (a price he can afford)?"
He conceded the point before I finished the sentence. Now imagine if the NFT also came with the royalty rights of the song (not that this Grumpy cat came with that, but NFTs can be created where they carry rights with them), wouldn't he be willing to pay an even higher price?
Of course if you are selling to him something he already considers valuable at a very very low price he is gonna want to buy it. It has nothing to do with it being an NFT.
In short, he conceded no point but you did: the NFT in itself is not the valuable part, what's being sold is.
From what I can see, pretty much everything getting hyped with NFTs can already be achieved without them.
Blockchains can produce stronger guarentees than trusted timestamping. This is often used to prove digital existence and ownership.
Given the adoption of this interpretation in law disputes about digital ownership can amount to a digital signature with the private key.