From the Github docs: "If you publish your source code in a public repository on GitHub, according to the Terms of Service, other users of GitHub.com have the r

From the Github docs: "If you publish your source code in a public repository on GitHub, according to the Terms of Service, other users of GitHub.com have the right to view and fork your repository." So by using GitHub, he has implicitly 'signed over' some rights to other GitHub users.