I've been finding co-pilot really useful but I'll be pausing it for now, and I'm glad I have only been using it on personal projects and not anything for work. This crosses the line in my head from legal ambiguity to legal "yeah that's gonna have to stop".
If this is the case, I can imagine people migrating of GitHub very quickly. I can also imagine some pretty nice lawsuits opening up.
From other comments, this developers "private" code was found in 30k+ public repositories with public attribution which is what created this issue.
Presumably your private code is not also present or leaked to any public repositories.