It’s understandable to be confused by it, I’m not sure why it makes you angry.

Even if you’re familiar with the idea that some portion of the population is hierarchy/authoritarian prone, it makes you ask why. Then the answer just takes you one step deeper - that they like to see others suffer. Why? Because it makes them feel like they have it better than someone else, and that feels good. Well why does that make them feel good? Etc.

When you drill down enough you always get to “that’s just the way it is”, which isn’t satisfying.

I suppose that’s possible, but the thing you say OP is not saying is literally a quote. So at best it’s worded poorly.

Whose authority says it’s not sufficient? If they say they are nonbinary, they are nonbinary.

You can’t gatekeep being nonbinary. Not unless you’re prepared to define it explicitly, which will exclude many people - and not everyone will agree with your definition either.