Great observation. I always assumed the self-weight compressed the foot-top. I really like your idea/explanation for how it likely was executed. Makes much more sense.It looks to me like they fastened the foot to the table top surface from underneath with a screw once the foot was planted and then tightened the screw frame by frame in order the compress the spring, giving the impression that the compression was as a result of the weight. This also kept the foot in place while they moved the upper body forward, and the knees were also locked at this point so once a foot was on the ground it was hands-off. My 2¢.
Such clean work. How was this made by human hands?