I had to search for 3 pages and watch 4 videos to finally find an audio demonstration on your video. So uh... what's the function of each potentiometer?
Sounds to me like 1bit square waves. You can't get more digital than that. Anyway, all synths that digitally modulate their sound source should be considered digital (even if it's just DSP effects like reverb). Audio geeks consider synths that generate the initial wave sound with a VCO to be analogue - which doesn't make much sense, but that's the generally agreed definition. The sound demo is rather stupid, you can get analogue waves out of the PWM outputs on arduino, you just need to build a low pass filter. Which this kit already sort of does, I think. I don't have it so I can't check, but the opamp + capacitor could already work as a filter, or be wired to be one. Anyway, to be a synth, you need to implement at least attack and decay parameters, in addition to frequency.
