It might not even be "10 other people". For projects which originated outside Github, it's common for multiple users to have independently uploaded copies of the project. There's probably at least 10 users who have pushed copies of the GCC codebase to Github, for example.

> at least 10 users who have pushed copies of the GCC codebase

That is "10 other people". (Although your point stands, since there doesn't (or at least shouldn't to the point of criminal espionage) be any strong impediment preventing one person from creating 10 different accounts.)

It isn't "10+ other people wrote that", though. It's the same work, by the same person, being represented 10+ times in the training corpus.