Yes that was a good little video to see, thank you.
It appears that rolling the balls repeatedly up a series of spiral channels eventually forces them to self wear and become spherical. I wondered if any grinding paste/suspension was included or if their own grit did the job? I think they mentioned lapping paste for the final polish.
I thought I read many years ago that early ball bearing manufacture involved dripping molten steel from the top of a tower, with the molten steel forming a ball before it cooled and hit the sand at the bottom? or have I muddled this with another process?
I think that Britain has never (?) had its own ball bearing manufacture, which is why we were in trouble for the two world wars. Industry was using imported metric bearings in the 1930s because you find them in otherwise fully imperial motorcycle parts.