Even if the landing was a little bouncy, it's a landmark achievement for model rocketry. Tickled to see the top Youtube comment is from Scott Manley.

The mechanism to throttle the solid rocket motor is simple and ingenious - ceramic "jaws" underneath constrict to block a portion of the exhaust plume (an idea borrowed from Josh at Simple Robotics). Here's a link to the juicy bit in an earlier video on it, although the whole thing is worth watching: https://youtu.be/8sksiYfkses?t=658