That means Bearetta is following five accounts that muted that message, and the app muted it for her as a recommendation. It can be disabled by the user, and it does not affect users which dont follow the same accounts. I get your point, if someone creates 5 accounts they can mute a message for their connections, but this only works if their client is configured with this option, and if you make someone follow 5 different fake accounts. It is not censorship