Disabling submit buttons is an anti-pattern! How do people with low/no vision know what is going on? As the article says at the end, a far better UX is to show an error message rather than disable the button.
The article, however, is about the declarative and data-first approach that React takes to everything and its application to this specific case. It's not a UX piece, it's a tech piece.
Fwiw, I have a post on instant validations linked in the end.