Agreed. I saw this and thought it looked beautifully passive aggressive

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.