I think this is the crux. It doesn't matter that they used GPL code for training. It only matters if someone uses CoPilot to make a close copy of that code.
Fortunately Copilot is actually not commonly just copy/pasting. They did a study on that if you search for it (admittedly not an independent study but it's the only one we have).
> Why include that?
Because so many people are making the assumption that the law agrees with their overly simple interpretation before it's even been decided. It's a bit tedious.