I don't know if they mention it in the videos, but I think that some of these images were printed using Polaroid's "Vectograph" 3D print system. This was a system that Edwin Land and co. developed just prior to WWII.

It's a method that allows 3D prints to be made on a 2D surface, and viewed with polarized glasses by reflected light. It's a really interesting process that I just learned about recently, and apparently there was a move to reintroduce it a few years back with an inkjet variation.

Basically, you have this "vectograph film", which is a substrate coated on 2 sides with PVOH (polyvinyl alcohol) that has been stretched and thus molecularly aligned at 90 angles. Using dye-transfer matrices, you transfer special dyes to either side from the left/right images, and the interaction of the dye with the PVOH makes only the image areas dichroic, in the polarising sense. So the dye itself becomes the "polarizer", and with a reflective backing that retains the polarized light (aluminum paint) you are able to use typical 3D glasses just like you would view a 3D movie today.

Monochrome images are easier, but they did indeed find a set of tri-color dyes that had this property; allowing for full 3D, full color images to be viewed like a regular print.

Amazing stuff!