Creator, or proof reader ?

The key to understanding this is that copyright covers "works". So if you take the kernel source, make some modifications and publish a tarball, you own the copyright on the tarball ("the work"). That doesn't mean that you own the copyright to every line of code inside that tarball. Someone could download your tarball, delete your modifications add different one and create a new tarball and now their tarball has nothing to do with yours.

Just cloning a repo doesn't create a new work though, because they're no creativity involved.

In fact, one of the features of open-source is that the copyright status of a lot of code is somewhat unclear but that it doesn't actually matter because open-source licences mean you don't actually need to care. If you make a single line patch, does that construe a "work" that's copyrightable? If you work together with someone else on a patch, can you meaningfully distinguish your copyrighted code, your coauthor's or the copyright of the code you modified?

Copyright law has the concept of joint-ownership and collective works, but copyright law doesn't really have a good handle on open-source development.