This is incorrect because it conflates non-fungibility with uniqueness. That is to say, if Jack Dorsey wanted to, he could simply mint /another/ NFT of his firs

This is incorrect because it conflates non-fungibility with uniqueness. That is to say, if Jack Dorsey wanted to, he could simply mint /another/ NFT of his first tweet. Now, whether he does this or not is sorta up to him, but it's possible. As other folks have said, it's similar to an autograph or limited edition trading card rather than a one-of-a-kind.