Find it amazing that he assumed 8 times too much density, but still the design in regard to lift missed only 50%? Not too bad, likely had quite a margin planned as good engineer? ;)
Also have to take into account that number was at ground level where there is the highest air density. I’m not sure what the landing and takeoff profiles looked like in the design but presumably the wings are that size so it can operate at a higher altitude at a reasonable speed.