The main difference is that htmx is server driven, and it's HATEOAS (hypermedia driven). Angular was always client side only with data binding and state management. So as far as frameworks go, they are pretty much as different as they come.
Where code runs is a small, albeit important, part. Whatever you use "Hypermedia" or JSON to communicate the state is only part of the story. What makes HTMX a second attempt at Angular 1.0 is in how it handles mutating the HTML, you know, the key aspect of a web app. Splitting some of the FE to backend to allow room for the spaghetti we had back in the CGI/PHP day isn't a win.