Here’s how to reproduce :
Rings in second mode (“sitar” mode). Structure knob to 9 o’clock, so it resonates to the octave below the played note. Max polyphony (red light).
Use the external input, in my case with a noise source. Short trigger in Strum input.
Now change the polyphony, to either 1 or 2 voices : the pitch of the resonating string changes to one fifth below. (and it’s really hard to find a sweet spot to catch an octave).