According to google, the first thing that makes a web-app progressive is the ability to work on ANY browser (this includes text based and that don’t have JS turned on that people still use!) https://developers.google.com/web/fundamentals/getting-started/codelabs/your-first-pwapp/

Yes it also does include things like offline functionality which you have in your article, but I don’t see that it is fully progressive? In other words, will it still work if JS and CSS is turned off?