Around 1979, the company I worked for purchased a CNC mill to manufacture sideplates for the printing presses we built. Before then, printing press side plates were typically bored in pairs so the printing cylinders would be guaranteed to be parallel. A customer questioned that our method of manufacture was sufficiently accurate. The accuracy was demonstrated by placing 2 sideplates on top of each other, located by steel dowels in matching holes. We then placed a 6" diameter ball bearing in the upper plate, and it slowly slide down and into the lower plate without hesitation. This was repeated for all 3 cylinder locations. The customer was convinced.
I suspect that the pieces in the video were EDM (Electric Discharge Machined). That type of demonstration was typically used to show the accuracy of the process.
Good judgement comes from experience.
Experience comes from bad judgement.