Effectively, what a proxy does is that it hides the original connection of the user and provides a different one.
Instead of someone using their own IP to connect to a service or web page like FeralHeart, they instead go through another server first and use that IP over their own, this means that the IP they use, isn't really theirs.
IP > IP > Site
While it should be.
IP > Site
Most browsers have a settings page that allows users to set up proxies, and they can also be temporarily disabled just as easily as they are turned on. Your friend would need to disable their proxy in this case.