I'd guess that it's a combination of things:

- The material of the robot's "finger" makes for a very clanky sound (metal?). Actually it sounds kinda like a harpsichord - The perfect rhythm makes for a very robotic feel - The perfect consistency of how a string is plucked (same attack/volume at every note) also makes for a very robotic feel

The first is about harmonics, the second two not so much, but I'd expect that harmonics are the lesser of what makes it feel midi-ey. After all, some people play with metal picks or fingerpicks (https://en.wikipedia.org/wiki/Fingerpick).