They found ancient inhabitants of Georgia using iron ore as flux for copper smelting, so it's a theory of how they went from one to the other. It's not terribly exciting but it beats "they tried smelting rocks at random to see if anything good would happen".
Smelting random rocks (with fairly distinct appearances) sounds like a very logical thing to do. I would say it's a natural human impulse to experiment with random stuff and see what happens, that's curiosity.
What sound highly improbable is someone having access to this obviously different ore (used as a flux) but never thinking of smelting it.
Having been a kid living in a place that had open fires burning (new houses were under construction and the builders often made fires to get rid of scrap materials), I can say that the desire in the primitive mind to throw random things into a roaring fire to see what happens, is strong.
Is there any theory how it could have been any different?
It sounds obvious, that advances in metal working comes from those working with metals and not from carpet makers.