Gender is about grammar and pronouns. It is a lot more important in other languages than English, and often has nothing to do with sex. There are languages where the genders are "alive" and "dead", or "adult" and "child or animal".
To reiterate one of my other comments, the time of appearance and usage of the terms show how language changes over time. As of yet, I'm unaware of "homogender" and "heterogender" terms, although they can be translated directly into known/existing sexuality categories that aren't the same as heterosex and homosex.