While the video itself was also titled to be a “3D Printer”, it really is more of a milling machine: it doesn’t add onto a base (like ink to paper or plastic “glue” for 3D printing), but reduces/removes bits of a material on top to get the desired shape.
Oh, and, it’s done with LEGO
Were you also surprised by the resulting quality of the mill process? It’s getting quite impressive to see what creative people are doing with more “serious LEGO”, and while the process seemed to take long, it’s likely one that can/will get improved over time to ultimately compete at being able to quickly prototype anything in 3D.
Taking it a few steps further, these improvements could start to form the basis of home-based prototyping studios. 3D printing (with the use of plastics, “printing” an object in 3D with plastics/synthetics layer by layer) is starting to see use by hobbyists, and tend to still be noticeably “printed” with lines/layers of plastics. Milling to this detail can help prototype an object in higher detail.
If you were interested in this sort of serious LEGO project, you might also be interested in this too (link).