Honestly, I still got a huge box of Lego in my basement, but I do not recognize half of those parts he is using for those tanks. They appear all new to me.
Plus: he is using an awful lot of flat tiles for the tank bodies.
In my days those were so rare, I had a very limited selection, evenmore in many different colors only. Sometimes you bought a whole kit for a single modern brick you wanted desperately. If I would have had that assortment of bricks, who knows what I would have created.
And I admit, my lego aircraft carrier was a bit out of scale, but still I had a lifting ramp, retractable wings and rotorblades on airplanes and helicopters and a well deck for landing crafts. 
Those smooth edges are not from that 'flat tiles' but rather a "house roof" like bricks.
IMO, this kid is doing great. They are all on-scale, even with the standard size human lego figures (go check out his M3A1 halftrack).
Regarding the customized bricks: well, he used most of them creatively. For instance, check out the detailed tank tracks and cannon designs. He mixed Lego Technic parts with regular system/themed parts.
