Great idea, great video!
(Naturally, it is based on the fretted Clavichord. The defining element of both is that each “key” not only sets the string in motion, but also determines the “Speaking length” of the string. In other words, one string creates multiple notes, as opposed to a harpsichord or piano which has an individual string for EACH note. In the case of most clavichords, one string usually is played by only three or so keys, so there are more strings than this simple version, but of course, less than a similarly-sized clavichord or piano.)