It is because the presence of a front push pin on the receiver (Without a denial in the receiver like on MKE guns) makes the gun a machinegun irrespective of a semi auto only trigger pack because in 30 seconds you can put an MG pack on it.
Its possible (would be a small chance) that it is a flat that was folded to look like a clone and then registered as an SBR. If you want to IM or post pictures I could tell for sure.