I believe the system queries that information based on the login, but I’m not 100% sure, and I’m not aware that anything but your selected Country/Flag can be viewed from Zwift or Zwift Companion. To my knowledge, there’s no way to update the City and State information in the Zwift settings. If it does appear anywhere in Zwift, it would be automatically generated (albeit seemingly incorrectly in your brother’s case) by the system. You can change the country (dictates what flag you fly in Zwift) in the Zwift settings but no other locale options are currently available.
Please provide us with a screenshot of where you’re seeing this “Easton, Massachusetts” information appear in Zwift, and we’ll be happy to further investigate the matter. Thanks!