I'm not sure if it's the law or just common sense. The new plumber said he wouldn't be happy leaving the pipe as shallow as it is. It's some places the pipe isn't buried at all.
My comment related to the old plumber. Pay thr new one obviously. The ild plumber broke atleast two bit of the law. Safe goods amd satisfactory quality. He probably broke the bit about being as described. soooo...
DO NOT PAY THE ORIGINAL PLUMBER. HE BROKE THE LAW. SCREW HIM.