Test after log out.
Any post attempt is met with the login page.
That these posts after an account is deactivated are listed as being from that disabled, formerly real user, means they can't be from a guest.
These email as user name accounts can not be searched for.
Typing all or any part of the user name (the email) does not return that account with the email as its name.
This all looks more like system file manipulation.
Owen