Zero tolerance machining examples - GIF

[imohtep56]

Back in the 80', I was at a steel supplier picking up some material. At the counter they had piece is about 1/8" thick steel plate laying on the counter. It had the profile of a circular saw blade drawn on it. I picked it up for a closer look. The parts fell out. I was holding what was left of the square. Laying on the counter was the blade and the "hole" from the blade.

I am curious what process was used in the video to leave no lines at all?

Usually EDM- this inner and outer parts are cut from 2 separate blanks...