You can wipe your ass with the GPL license if your use of the product falls within Fair Use.
You can actually take snippets from commercial movies and post them onto YouTube if your YouTube video is transformative enough for your usage to be considered fair use. Well, theoretically at least - in reality YouTube might automatically copyright strike it.
>Copying and storing a book isn't recreating another book from it.
That doesn't mean that GitHub has to redistribute Copilot under GPL. However, the end user could potentially have to if they use Copilot to generate new code that happens to copy GPL code verbatim.