It’s basically like a copy of the original repository. But you can pull in and merge changes from the original, make a pull request for the original to pull your changes. Fork+pull request enables you to contribute to someone else’s repository. Things like Chromium are in part forks of Safari, just that they diverged over time.
By the contract, you couldn’t say anything detrimental about the game, so such a statement would still be forbidden. Whether such a vague limitation on what a content creator can say would hold up in court is a different thing.