So everywhere except for Russia, Ukraine, Belarus and where there's no data.

Also a bad choice to put no data and no on the same color.

I'm guessing that this just means that there's at least a single school willing to teach it, it certainly isn't all of them.

That doesn't mean a whole lot. If one school in the country offers an elective, is the country highlighted? Certainly we didn't have widespread classes in ancient anything.

this is simply wrong, probably for all countries besides Greece itself. I never had it in school and I never heard of such a thing.