If it wasn't a restricted area, you weren't holding anything in your hands (and you weren't scanning them) and you didn't resist a scan by the guard (which will happen if they try to scan you but you move away) then I'm not sure what it might be and it might have been a bug.Not sure. But how can it be restricted if the security in the area is Level 0 (which has meant that anyone can enter at every other place I've been to, including in the Alpha)?
Upstairs, there is usually higher security areas, but I was not far past the entry into the HAB