No, it doesn't mean only humans can interact with it.

The key point [of classical REST] is that responses are self-contained self-describing. Requesting a resource response tells you what actions you can take on it. There is no need for application domain knowledge, implicitly or separately-explicitly shared knowledge.

Some HTTP web apis offer links in their JSON responses for example. Like previous and next page/ref on paging/sectioning/cursor. Or links to other resources. I don't think I've ever seen possible resource actions/operations be included though. Which is what the original REST would demand.

That's how I understood it anyway.

Their suggestion of using HTML rather than JSON is mainly driven by their htmx approach, which the project and website is about. Throughout this article though, they always leave open which data form is actually used. In your quoted text they say "for example". In a later example, they show how JSON with hyperlinks could look like. (But then you need knowledge about that generalized meta structure.)