You can't really train a chin to come when called, lol, they are kind of like a cat in that respect. They come if they feel like it and there is something in it for them. Like most will learn to come to you at the cage door to be let out. Also they can get into trouble so quickly that it's really never advisable to allow out of cage time if you aren't right there watching. Unless you live in a house with no electric cords, nothing unsafe to chew and eat, no appliances, nowhere that chin can get to that you can't reach, etc, then a house really can't be chin proofed enough for unsupervised play.
Unfortunately people do some pretty stupid stuff with chins and post it online. A lot of times the people posting the videos that say "oh my chin is trained and free roams the house we've never had a problem" and then sometime later they come back crying that their chin chewed an electric cord (or something else it shouldn't have), or got stepped on or sat on, and died or is seriously sick or hurt, or is loose in the walls or managed to get outside somehow.
As for the pooping, chins should always be pooping, a healthy relaxed chin poops about every 30-90 seconds (unless they are asleep). You can potty train most chins to pee in a pan, but they don't really have control over their pooping. If their digestive tract is working they are pooping. The only time they seem to be able to hold it is when they are stressed, like it's common for them to not poop while at the vet for example. My guess is either the chins are stressed due to having free roam of a large area where they aren't sure if there are predators. Or the poops just don't show up well in the videos and/or the video is taken when or where they haven't pooped much yet.