"Ghost" Guest User Account

Hey!

I recently purchased a used MBP and did a fresh (format hard drive + boot disk) install of OS X High Sierra. I am currently showing version 10.13. The format was with APFS (Encrypted.)

Since installing High Sierra I have noticed a strange Guest User icon on the boot screen. It is not the same as a normal Guest User, and clicking on it opens a dialog for a password (my account password and my disk password do not work here.)

Here is the icon that I am talking about. If you zoom in on this image you will see that there is actually some slight noise to the icon like you would see on an older TV. There is no movement to the icon, but the noise in the icon image changes every time I reboot the computer.

I do not have a guest user account enabled. See below.

Above is a screen capture of my users and groups. I have tried turning the guest user on and off and restarting my computer many times to see if it's just stuck somehow. No luck.

Above is what it looks like when I have the guest user turned on. As you can see, the icon is correct and clicking it properly restarts the computer in "Safari Only" mode.

Thanks in advance for any help, this is quite frustrating.

Grady