There are User Names and there are Account Names. User Names are specified in Preferences and Account names are specified in Manage Security. They can be exactly the same text, but adding and using a new Account name does not automatically change the Username specified in Preferences. I Filemaker confuses this fact by automatically entering the User name as the default account name when you first open a password protected file.
I suspect that what you see in the log is the User name and thus you see the Admin user name instead of the new account name used to access the database.