If the structure is made of steel columns and beams *and* the floor is steel plating, brick, or concrete then the contractor is correct. Otherwise, he is so wrong as to raise concerns over his competency in other areas, as well.

Perhaps he means a mud pack pan for a preslope and a waterproofing membrane on top of that, with tile as the finised surface. Some people confuse that with ''cement'', which technically is the binding element in concrete, not concrete itself. A mud pack pan can work wełl IF it is done correctly. You need to ask more questions to determine exactly what method is being proposed.