Centaurs from Greek mythology are largely believed to be derived from people of the eastern steppes who were nomadic horsemen. This isn’t because Greeks never had seen a person riding a horse before, but because over time a group of peoples who are exceptionally gifted riders become half-horse in the mythological imagination of the people who retell these stories over several generations.
I have never read 1001 Nights before, so this information is second hand, but as I understand it the djinn (genie) living in an oil lamp was not originally a part of those stories or Arabic folklore, and was added much later.
