Well, it is what it is. Unless the scale wasn't accurate. A few things come to mind compared to the 2012 weight sheet.
Did 2012 models have DEF, DPF systems? That adds exhaust components as well as def holding tank, pump and associated plumbing, wiring.
I noticed poking around underneath that the air compressor and tank for the air ride is pretty big. Also there is still a spring pack along with the air bag system. All that must weigh something. Truck also came with 5th wheel prep which wasn't offered in 2012, so that may add some weight for the structural members in the bed.
Again this weight also included torklift frame mounts which were pretty beefy, and running boards.
Other than that I really haven't a clue. The fuel tank was 1/4 tank and the truck was empty. I was going for lowest tare possible without going to the trouble of removing the torklifts, spare tire, back seat etc.