Devil Fruits Had a Different Name Before
Modern Era
= The Celestial Dragons are treated as Gods
= The Descendants of the Ancient Kingdom are treated as Devils
= The Devil Fruits come from the Ancient Kingdom
Ancient Era
= The Celestial Dragons were treated like normal people (neither Gods nor Devils)
= The Ancient Kingdom was prospering and Joyboy was treated as a God
= ???
It may be likely that the Devil Fruits were not called by that name in the Ancient Kingdom. Instead, they are likely to be called Divine Fruits.