To quote from the article: "These repositories, belonging to more than 16,000 organizations, were originally posted to GitHub as public, but were later set to private [..]" Once things are public, they will forever remain public (in some form). That's how the internet works.
Copilot is a code completion, and authoring for developers.
It’s not a presenting a copy of trained material, rather generating new content based on what it has learned in the context of the problem / query discussed in the prompt.
Repositories available (complete copy) sounds more like a search engine cache, which is mentioned in the middle of the article (Bing).
So, is it Bing, the search engine or the AI model?
Perhaps I am missing the core here, but at the moment it seems like a Bing story dressed as AI story for traffic (arstechnica) and fame (lasso).