Obviously (to me) it was called jews harp because the instrument is played by people all over the world -- people representing EVERY COLOR ON THE PLANET. They could not, very easily anyway, call the thing the colored guy's harp without the cry of total racism being raised everywhere.--- So they settled on calling it jews harp after those folks over there. Remember, them that called it that had no idea that the Hollocaust was gonna happen. Nobody did. But when those sad events did occur, alas, there were none of the guys from the 1500s who named the thing to take back their inapropriate nomenclature. It's nobody's fault.
But just try to tell that logic to Oedipus...
Can't be done.
(And, yes, I'm Jewish. At least half o' me is.)