Why randomly generated instruments?
DF is eventually expected / intended to procedurally generate entire fantasy worlds. It's already closer to that than any other software I'm aware of; but procedurally generating *cultures* is a seriously under-explored area.
Music and poetry, sometimes combined into song, is one of the most powerful and obvious differentiators of culture. Toady is working on procedural generation of all three, and that is going to be very interesting to see how it works out.
And as for your other objection, most people are not familiar with real pre-1400 (or even pre-1600) instruments by either name or sound. Without looking it up, which of the veena or the bandora is ancient, and which is mid- renaissance and technically post-period for DF? (1) If someone referred to a "wait-pipe", what then-common instrument would that be? (2) And of the salpinx, sackbut, aulos, and zampogna, which would have been the companion instrument implied by that description? (3)
How many of those simple, common, examples has the average DF player *ever* heard played... heck, how many of them has even the average music historian even heard played? I've enjoyed live performances of
Piffaro, an awesome renaissance band which occasionally dips back into late medieval, and they perform with a bewildering variety of instruments most people have neither heard, nor heard of... and most of theirs are several hundred years closer to familiar modern instruments.
tl;dr: Procedurally-generated cultures demand ways that the cultures are different, and music is a great way to show that. Additionally, most actual historical instruments have strange names and stranger sounds to modern players, to the point that in a listing of dulcian, krumhorn, launedda, fiblergausth, swarabat, tiexianzai, charango, grajabpi... does your invented "fiblergausth" look any stranger? (All of the others are real historical instruments.)
(1) The
veena dates from antiquity (shows up on coins from mid-300s), whereas the
bandora is believed to only date back to around 1560.
(2) The "wait pipe" was slang for the
shawm(3) The description implies use in a medieval or renaissance ceremonial European town band, which would typically be comprised of shawm and
sackbut players.