Yeah, those pages are definitely auto-generated. Static site generation makes it possible for those types of pages (I call them "shims") to jump to the top of the results list. I wrote about it here: https://zestyrx.com/blog/nextjs-ssg
The difference in speed between running a simple script and reading a file is not large enough to noticeably affect SEO.
Most of these sites are probably just using PHP, not any static site generator.