In my head, a static page is something that's served verbatim, without some backend generating it or inserting things into a template.
Wikipedia seems to agree with that view: https://en.wikipedia.org/wiki/Static_web_page
Otherwise, all of the React server side rendering is static HTML.
If you pre-compile the HTML using something like Jekyll, so that the webserver is just serving HTML files without any dynamic/on-the-fly processing at request time, then it's considered static.
React on the client side: static, as you still got the same files served, how they dynamically alter the page runtime doesn't count.
The issue is whether they are being generated dynamically by a server. This project isn't. You run a build-tool once and then can post the .html page anywhere. It's static.
CSS and JavaScript and images are also static, it doesn't have to be just HTML
If you have a perl or bash or c backend generating html in response to http requests it's not static
'Static' means it's only made of static files that can be served by just a vanilla Web server (i.e. just by serving static files).
The combination of all of these direct a browser in how to render a page.
Traditionally, a static site or static page is one whose data can be delivered to the client directly as stored, with no server-side alterations or generation.
This is/was a meaningful distinction because a server that can stream stored data is fundamentally much simpler than one that executes programs. Such a server can run in different contexts, be optimized in different ways, and satisfies constraints that allow further optimizations downstream.