From the Copilot FAQ, notice there is no specific mention of the term "Open Source": > It has been trained on a selection of English language and source code

From the Copilot FAQ, notice there is no specific mention of the term "Open Source": > It has been trained on a selection of English language and source code from publicly available sources, including code in public repositories on GitHub. Meaning GitHub might have also been sourcing from public source / source-available projects that were not OSS licensed at all.