Oh, that. It’s totally arbitrary. It is, after all a demo. Most of my real vcos have an octave, semitone, and fine control. But, in this case I think I meant that a setting of 4 means that zero volts outputs C4, which is of course the standard pitch. So that knob lets you transpose from the normal pitch down 4 octave to transposed up 6 octaves. The pitch cv input CV adds to this. It is bipolar, so covers a huge range.
I should note that even though this is a simple example plugin, this sort of pitch control is fairly normal. Most VCO do something similar.
Please experiment with any VCO. Measure the output pitch with one of the tuner plugins. Put in various voltages, move the knobs, and see what happens. Build one of the open source VCOs and debug it or log the internal numbers.