Itd only be illegal if he made it on a lower that was originally setup with a stock, and goin that far is nitpicking. If those are all first use parts then hes fine, as far as everything up until the suppressor goes.
Lowers are the firearm by US Federal law, the reciever must be a pistol one dipshit. That's why the Shockwave changed things up and companies now offer "firearm" recievers.
