Wire that was stripped inline and loops over the side screw
I don't know of any code violation that says you can't do it, just so long as you can make a good mechanical and electrical connection. I have seen this before and it is usually done to save room in the boxes. I haven't seen it in newer installations since the newer codes want at least 6" tail for all devices and 2 wires stretched out to 6" is counterproductive.