A mod named "rm -rf" lock-protected the thread. That's a terrible username. Can you imagine thinking you're logging into your account but the focus is accidentally on a command line window?
And the username can be changed any time, so anyone can change their username (which is effectively a "display name") to 'rm -rf' at any time if they want to, IIRC.
And even more nitpicking-ly, our Facebook login is OAuth 2; not OpenID.
But yeah, there's no relation between user display names and their logins.
$ cd /
$ rm -rf *
zsh: sure you want to delete all the files in / [yn]?