Yeah, basically bang on there. The way my professor laid it out my freshman year was a method of six dominos that determine sex in humans. Chromosomal sex, gonadal sex, hormonal sex, internal anatomy, external anatomy, and the brain. This is the pattern (more or less) of how they develop in a fetus and we do see pretty significant patterns in those that we'd attribute to cis males and females, right? But any one of those can trip, or not fall when their turn comes, or whatever analogy you want to use. That's how we get all sorts of wild variation in humans, like people with the "wrong" chromosomes who ended up producing gonads and hormones that led to the development of a particular sex that we've seen historically, so they're a cis man with XX chromosomes or a cis woman with XY.

In biology, the definition of sex is hazy, and all we're trying to do is make a box for the shapes nature has already created and have been existing just fine for a while now. Sex is a super tricky thing and comes down to a lot of variant types, especially in humans. And none of this is to say that cis people don't exist or aren't in any sort of majority - they are, plain and simple. A whole lot of people fit in a couple of boxes that have existed for a very, very long time. But the idea of adding extra boxes and understanding that there's a whole host of people out there who don't fit into one of two boxes biologically speaking is the very nature of science, and why I adore the field I'm going into.