That's common in old barns too. They used to run cleat or knob wire the length of the stalls and just pigtail a socket on it wherever one was needed. Cleats seem to be more common with exposed wire. The switch was near the door adn turned them all on at once. If they were real fancy, they used cleats or rosettes and hung a corded socket with a turn switch or pullchain.
I've also heard the term "open or cleat wiring" or "mill wiring".
It must be somewhat safe because I've seen a few systems like this still in operation after 70 or 80 years.
