Static site generators have been around for ages. Jekyll was one of the first, as far as I know, but there are dozens of others now.
Sure, generating HTML via another language is not new, but SSG pushed back against the notion of using dynamic CMS systems (which were de rigueur in the early 2000’s) in favour of static pages hosted on serverless systems and like GitHub pages and S3, with content (mostly markdown) held in version control systems instead of a database.