He's doing it to raise a point about what self-ID'ing can lead to. Watching people tie themselves up in knots arguing against it with comments like "You're only born once, you can't change your age" to be challenged with "You're only born once, you can't change your sex" has, from what I've seen online, made people realise that maybe ID-ing as whatever you want isn't as simple as they may have thought.
I also do not find it coincidental that the media is running this story at the same time the story of the white man claiming he's black came out as both highlight the ridiculousness of the "I feel like I am, therefore I am" self-ID argument.