Note: If you publish your source code in a public repository on GitHub, according to the Terms of Service, other GitHub users have the right to view and fork your repository within the GitHub site. If you have already created a public repository and no longer want users to have access to it, you can make your repository private. When you convert a public repository to a private repository, existing forks or local copies created by other users will still exist. For more information, see "Making a public repository private."
It's not about forking, it's about forking with the intent to compete (which this was, as it was advertised as an alternative here). In that respect, regardless of the Github.com terms of service says, federal trademark law is likely to supercede it.
Note: If you publish your source code in a public repository on GitHub, according to the Terms of Service, other GitHub users have the right to view and fork your repository within the GitHub site. If you have already created a public repository and no longer want users to have access to it, you can make your repository private. When you convert a public repository to a private repository, existing forks or local copies created by other users will still exist. For more information, see "Making a public repository private."