Looks like someone enabled the hidden local administrator account which is typically disabled by default.
Maybe just open an elevated command prompt and type net user administrator /active:no
and see if it goes away.
How do I run a command with elevated permissions?
Some commands that you can run using Command Prompt might require elevated or administrative permissions. To run these commands, you can use the Run as administrator command.
Swipe in from the right edge of the screen, and then tap Search.
(If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then click Search.)
Enter cmd in the search box, and then right-click or press and hold Command Prompt.