One theory Ive read about is that they probably merely iterated on the (likely middle eastern, probably egyptian or persian) invention of "greek fire". Since its only a single ingredient difference between one of the known formulations of it.

And the Europeans made gunpowder useful with the invention of pearled gunpowder, which made it possible to predict burn rates and slow them down for cannons, allowing for bigger and more potent cannons. Anecdotally, there is documentation of an Ottoman diplomat pleading to a Chinese one that "the Europeans never learn to make gunpowder"

They also claim to have invented chariots, despite using the Sanskrit word for chariot.