I have the same problem with the plugin returning a positive response for "Admin".
My primary concern is that the plugin is checking not only on the register form, but also on the login form. I would prefer the plugin:
a) only block registration attempts, not login attempts
b) whitelist already-registered usernames
Optionally, it would be nice if the plugin could provide options to check for any/all of IP address, email address, and username, on any/all of register.php, login.php, and login-form.php.
Is this plugin still being actively maintained? I noticed that the wp-nospamuser plugin from which it was ported is at version 7.2, and was updated 2 months more recently than bb-nospamuser.