So I searched for videos explaining how he does this stuff. Found a few short bits. He's apparently big in the Spanish-speaking world!
I thought the reference I read of him optically printing meant he used an optical printer (a fancy piece of equipment), but he uses a meter-long piece of wood with nails sticking up for the perforations, special film stock so he can use a red light and sort of see what he's doing, and laser pointers and film enlargers for the light source, and cardboard and leather masks. He uses a meter-long 50-frame (2 second long) strip of film at a time, contact-exposing them up to 7 times. Then he hand develops each strip. It's insane