iOS web apps worked in a similar way with a manifest file that was specifying all the files that were to be downloaded when the page was added to the home screen and how long they were meant to be cached. I remember having created one 5 years ago and the technology was probably around for longer.

Maybe I miss something but the term Progressive Web App feels a bit like "Ajax", i.e. a marketing term for a technology that pre-existed as a way to promote it.