It is likely that the selector has been pinned to semi auto only and the gun assembled without the FA parts.
It's not illegal for a semi auto rifle to have a full auto mark near it's selector.
Here is a Vector D,E,S (German full auto Uzi) selector converted and remarked to semi auto.
This is a HK G3 trigger that has been "clipped and pinned" for use on a semi auto HK 91.