That user isn't banned, you can check in: https://bpip.org/Profile?id=2627711 if you are not sure. I guess you think that user is banned because they still have a mixer signature and avatar on, but that's not how the mixer ban works. Mixer signatures have been wordfiltered already and if the user doesn't remove it, they'd be blanked in a few days or so. A user would only be banned if they continue advertising mixer signatures and avatars, i.e. by wearing a new mixer signature or avatar.