With artwork it's hard to tell if that's how it went down or if that's simple an artistic representation designed to imply something based on knowledge shared with the viewers and if the latter then that opens up more questions. Is the artist doing it that way because "chariots -> foreigners -> bad" or it could be "chariots -> old ways -> inferior" or it could be "chariots -> obvious favorites -> underdog won anyway"

Kind of like how George Lucas made the empire look like the Nazis so you know who's good and who's bad in the first minute before you even know what else is going on or how in most artwork about the American revolution it's obvious which side is and isn't a professional army.