Im sure its not 100%, but I think the fuel cap is usually on the kerb side of the country in which the car is designed and built. THis is maybe if you break down, you dont need to walk out to the traffic to refill. Japanese cars have the fuel cap on the opposite side of the EU made cars, as they drive on opposite sides.
Maybe japanese cars made in the US alter this norm? Normally if they are made in Japan they would have the cap on the left as traffic in Japan goes on the left, the same as in the UK, India, Australia etc.
I have a Korean car, but its electric and the filler cap/recharge port is on the right., they drive on the right, so again makes sense, if anything does actually make sense here