Nice video find! Really have to love PVC.

Good vid. You can avoid having to cut the slit in the pipe by only pushing the  PVC pipe just past half way over the bead. With a little bit of trial and error you find out where tight and not too tight is, for  popping it off . If you want it looser in the joint, say for a string puppet head, that must be loose but not come apart, you can wrap the ball in a few layers of plastic shopping bags before you do the pipe, then pull the bags carefully out.

There was a follow-up video that showed why he cut the slit. He was using these ball joints as camera supports, and wanted to be able to pull the socket off the ball easily in order to be able to make a quick camera change.

it depends on how much friction you want in the joint, but it seemed to me that it looked pretty good as is for say, a rod puppet. That's actually why I went in search of a video like this. I'm hoping to move into rod puppetry, and I needed to understand ball joints a little better.

I really enjoyed both Shawn's series on a paper mache ball joint for a marionette and Philip's video on home-made wooden ball joints. I think this method is a little more my speed, and I can finally visualize how I would attach mechanics to manipulate a head.

This is just one more piece of evidence to the claim that the only right way is the one that works for you.

You hit the nail on the head... "the only right way is the one that works for you".