I'm pretty sure it weighs 81,000 lbs. The empty looking truck bed is easily explained by the weight of the batteries you need for a 500 mile range 81k lb vehicle. That's part of what people told him would be the issue with EV semi trucks, not that its impossible to do now but that its stupid to make one now because semi-trucks are meant to haul lots of cargo long distances. Of course his now became 6 instead of 1 year later but still some of the same issues apply.

If your semitruck is allowed 81,000 lbs but unloaded it weighs 70,000 lbs, it sucks for hauling cargo. Notice he never mentions anything about how much CARGO WEIGHT it can haul. Based on how heavy Tesla's current batteries are for cars (and yes, their cars typically run 25% heavier than gas cars of the same class), a semi truck with their specs would be ~15,000 lbs heavier than a full 2000 mile tank diesel trucks carry. Electric motors would also be heavier than a semi truck's diesel engine.

The 80k weight limit isn't a cap on the limits of a diesel engine, its the cap on how much they calculate roads/bridges/highways can withstand. The weight limit isn't a strongman contest, its because heavier vehicles damage roads. Diesel trucks can in fact haul well over 80,000 lbs. They don't because the law stops them. He's selling to an audience that's never seen a truck weighing station before or something.