Eh, do you honestly think historical fidelity ever once entered the minds of the people making this "game"? It's just going to be a Rome=USA, Call of Duty propaganda entirely performed through QTE's. Pretty much the same way 300 turned Spartans into macho American parodies, crying about freedom and liberty and fighting against tyranny, when they were actually some of the most disgusting slavers and eugenicists of the ancient world. Fascist social darwinians before the words ever existed.
Well, arguably that's exactly what the spartans did though. They defended their freedom (i.e. not having to bow down to a foreign power or worse, pay taxes) and their way of life. That their way of life was horrible, no question. But freedom and such aside, this are just words with many meanings. I am not quite sure that a rightwing American means "I hope that every person on the planet has the chance to decide himself what he is going to do with his life" when he says freedom. Explain the difference between slavery and people working under horrible conditions with hardly enough to get by and no real chance to get out. Which many right-wing Americans apparently have no problem with. One could make a longer list.
But in the end the thing is, maybe there's actually quite a few values that are actually important to the American Right in real ancient Sparta (more than in say ancient Athens). They were quite gay and pedophile apparently, which is unfortunate, but we have the artistic freedom of taking it out, since it does only distract people from understanding our message about how people awesomely fought for defending their way of life. There's also the crippled guy iirc, which is not accepted by them. This could be perhaps him working in the eugenics stuff, but then the cripple is also portrayed as corrupted ... some viewers might actually sympathize with that view.
I'm not saying the movie was good, it was fairly bad actually because 90% of the screentime was reserved for halfnaked men and halfnaked women barely showed up. Just wanted to rant.
TLDR: The shocking is maybe not that he has a completely flawed understanding about a culture with horrible values. It is that he (openly, secretly or subconsciously) agrees to a lot of those values.