A SPA is *generally *“rehydrated” DOM elements from JSON data pulled from an API though. Where as HTMX is more akin to classic AJAX style page dynamism.

You'll forgive me if I say this is an instance of splitting hairs and having a particular definition for something that includes extra qualities separate from what those terms are actually describing for most people. Also, things like, I dunno, React, are going to extensively use ajax to accomplish what they do. It's literally just asynchronous javascript. It's like someone saying "my vehicle of choice is a motorcycle" and then someone else saying "A motorcycle isn't really a vehicle. It's a transportation device with wheels. A car is a vehicle." They are both vehicles. They both have wheels. The wheels are ajax. A page made with htmx and a page made with React are both SPAs.