I largely disagree with this article, at least for MIT, BSD, etc. training code examples. The small autocompletions, even if they are several lines long, sort of seems like fair use to me.
I do think that CoPilot should have an option to use a smaller model just trained in code that has very liberal use licenses, because I think the use of GPL, etc. licensed code is problematic - at least for me.
For what it is worth, I have a lot of Apache 2 licensed repos on GitHub (largely examples from my books) and I am pleased if my code contributed a small bit to the CoPilot training data. I also publish my recent books under Creative Commons, allow reuse, even commercially licenses: basically anything I do that might help someone, I am all in for sharing.