I used to work in a factory that made these things for sale and that's exactly how we made them. What he didn't show is the first step in the process -- making brass rods out of brass ingots.
All kidding aside, there appears to be genre of YouTube videos which demonstrate how to make tools for your shop. There are videos showing how to make table saws, planers, jointers, all sorts of sanders, all sorts of clamps, etc. The point doesn't appear to be saving money. Why would you spend a few hours to make a set of C-clamps when, by the time you buy the all-thread, nuts, hardwood, and glue, to make the clamps, you've spent more than it would take to buy the clamps ready made? Answer: Because you can.