Napoleon wasnt a mathemetician in our conventional sense, he recieve no education in anything resembling advanced or conceptual mathematics. Rather, Napoleon was a trained artillerist, who recived an education in ballistics. This is an important distinction. Napoleon learned applied math, military math to help him become a better artillerist and engineer. He was taught at a military academy, by career officers. Napoleon's formal education was oriented towards the effective employment of his weapons, the practical side of math, so I find it unlikely that he would have devoted much effort to theoretical geometry. Rather, the claim seems to me to be the residual effects of Napoleon's genius in other fields, a sort of "Napoleon can do anything" myth.