My initial reaction was also "if I can talk to your software, that's an API."

Reading through the article, though, the author isn't advocating for "no APIs," they're advocating for minimalist APIs that use agent detection to "do the right thing."

Chrome tells the API that it can accept HTML, so the server sends data formatted inside of a web page, with an HTML table.

Curl doesn't send that header, so the server sends unformatted CSV. But you could send an Accept header to get the HTML if you wanted.

The benefit of this is that for most use cases, this will "just work."

The downside is, if you want to view the CSV in a browser, or the web page in curl, you need to know (or guess) how the server is deciding what to send you, and take the correct action. An API documented with OpenAPI, while more complicated, explicitly tells you what you can do.