I remember this sketching/drawing exercise to work on hand/line rhythm waaaaay back in the day via something similar to a book in the “Draw 50” or Ed Emberley series. In this case, it showed a similarly tutorial how to draw “perfect” scales and to identify symmetrical line patterns.
Recently, it showed up on an older episode of “Miami Ink”, I think. There was an episode where the infamously brilliant tattoo artist Ami James was giving an eerily similar tutorial on this sketching technique. Curious, indeed.