(Then again, that makes me think: does that mean you could use a modified copy however you want, as long as you only do it over GitHub CI?)
Instead, I'd read "copies of Content" as referring to copies produced and consumed entirely through GitHub's services, which can exist independently from the original. E.g., if you have a public repo, someone else forks it, and you delete the original, the other person can still view their fork on GitHub. They can also modify that fork through GitHub's services, e.g., by editing files via the website.