Yup, it's a skilled trade for sure. Very handy too, because you can get things flat by using this method (ie heads, engine blocks, etc.), and not use a machine shop. It was a skill that all good mechanics had back in the day. It's also useful for bearings and the like. The scraping process removes something like .0001 of an inch at a time, and for machine bed ways, the microscopic divots hold oil, so the mating surfaces can glide on each other. Even cheaper machines are still usually finished with a powered process called flaking, to make even deeper holes for oil. You can actually get stuff so smooth and flat this way that you could, technically, make gage blocks that stick together. Here's a vid I found that explains it better than I can.
https://youtu.be/REeGn4hN1Bg
https://youtu.be/REeGn4hN1Bg