Login in GUI before continuing into single user mode

When I boot into single user mode, I understand that all I should get is a terminal/tty like environment with root account logged in. However on my Macbook Pro (Retina, 2013, macOS High Sierra), I have to log in via the GUI first before I can access the Single User Mode. I do not have filevault enabled, and I don't think I have a firmware password set either (I'm not sure because the macbook belonged to another member of the family at first). Why do you think I am having to log in via GUI first, is this some sort of setting or something? Thank you for your help!