The device isn’t very practical, but it does add some flash to live music performances or it makes a cool music visualizer. The matrix is only 64×64 so you can’t really expect it to match a proper scope. Besides that, it pulls its data from the Pi’s ALSA sound system.
You can find a video of the device on [Thomas’] Reddit post and a few additional videos on his Instagram account. Looks like a fun project and it also serves as a nice example if you need to read data from the sound card or drive that particular LED matrix.
We might have opted for PortAudio if we had written the same code, but only because it is more portable, which probably doesn’t matter here. Of course, you could also use GNURadio and some Python to drive the display. As usual, plenty of ways to solve any given problem.