There is no way to tell, from what you said. But I have had my XB6 for several months and neve had to change the userid/password.
I have escalated your issue to the Comcast Team available to these forums. Check back often for a reply in this thread from a Comcast Official Employee.
Hi JennaHissam, thank you for reaching out but from what it sounds like the gateway username/password didn't need to be reset. Please follow this link for instructions on how to change these back.