In the description it does not say it comes with the lower. If they shipped a working lower to him then I would think it was a mistake and definitely not legal.
You are bidding on a NOS 5.56 caliber SAR-80 (Singapore Assault Rifle) Parts kit All Parts kits are cut from the new unissued guns. All kits are from the same NOS weapon. Includes [all] cut Upper Receiver pieces, all demilled barrel pieces, piston drive, recoil springs, & one magazineBlack wrinkle spray paint finish