That is amazing. I never thought of using PVC pipe to build models.
It is a plastic resin, just like any other plastic resin. It just comes in a hollow circular shape. While I have not used to make scratch built models, I used PVC pipe material for modeling and non-modeling (non plumbing) projects.
The guy in those videos is a very skilled modeler who can make nice models from some basic materials and home-made power tools. He is also making profits from his videos. Probably his full time job.
I've seen videos of guys making similar scratchbuilt models using plastic from empty BIC disposable lighters. If you live in a place with no hobby shops, you learn to improvise. But I still think they do this to earn money on Youtube. Not that there is anything wrong with that.