The trick here is that we're looking at dogwhistles.
To someone outside the theater of culture-war this takes place in, this looks like a series of perfectly ordinary statements. Of course sex is binary, and that statement doesn't sound like it conflicts with gender being a spectrum, because sex and gender are obviously separate.
However, to someone who has lived within this theater of culture-war--who have been dealing with this rhetoric as rhetoric, which is what it is--this is a red flag. "Sex is binary" is the opening salvo in a common rhetorical strategy, which goes "Sex is binary, you're either male or female" -> "I'm just stating a fact, no need to be defensive" -> "See, this is why I don't trust trans people" -> "This is why you shouldn't trust trans people, they contradict basic facts like sex being binary". Notice the magic trick here--by picking phrasing that's plausibly deniable, and then framing any reaction to it as "disagreeing with Science", this guy can make it look like he's disagreeing with trans people, and make it look like trans people are somehow in the wrong for this, without ever actually having to stop and explain why.
That's not even getting into the fact that, frankly, "sex is binary" isn't actually correct. There are plenty of examples of species that don't actually fit into a binary sex model correctly--species which can reproduce both sexually and asexually, species which can change sex in order to find mates more reliably, and even cases where more than two sexes can be observed (such as in bees, for whom "worker", "drone", and "queen" all have different sexual characteristics). This goes against what most of us were taught when we were young, but that's part of the rational approach to the world: sometimes the model that we were given when we were in elementary school is wrong, and a newer model is a more accurate description of what's going on.
And that's part of the goal, here. "Sex realism", here, has nothing to do with reality, just as "religious fundamentalism" rarely has anything to do with the fundamentals of whatever religion is involved. Rather, "sex realism" is a rhetorical strategy which uses the aesthetics of skepticism to make one's argument seem sensible, polite, and rational. It relies on the audience never actually questioning whether the "sex realist" is describing reality, or reading beyond the face value of what they are saying.
The especially insidious part of this tactic is the way it weaponizes the reactions of people who understand what the dogwhistle means. People like me, who have spent hours upon hours discussing these things, immediately recognize the tactic at play--and more often than not, react loudly and angrily. After all, I've seen this conversation play out over and over, and invariably the guy claiming to just be a sex realist turns out to be an asshole, just like how the guys who claim to be "race realists" inevitably start citing things like the 13/50 argument (which is a whole other can of bad-statistics worms). But that's part of the plan--when I or someone like me says "What the fuck, get out" in response to the initial statement, that's when the sex-realist turns to the audience and says, "See how upset this person is over these definitely true things I just said! Clearly, if they're losing their cool this badly, I must be right!" And this works, because it short-circuits past the part where the sex-realist's argument is evaluated. By framing things in this way, the sex-realist can convince members of the audience to trust him before evaluating his argument, which lets him avoid actual scrutiny of what he's claiming.
TLDR: Wright is framing a simplified, not-really-correct statement as absolute truth, and then framing the people he opposes as unreasonable and irrational, to take advantage of the fact that human beings use trust to save processing power and avoid having to actually evaluate arguments.