Surely having ADHD would only give insight into whether it can be learned by someone with (that type of) ADHD, it doesn't speak to whether it's natural or learned for other people - just as someone who has a physical disability not being able to learn to ride a bike wouldn't prove that riding a bike can't be learned?

(I'm not arguing for or against the point that they can be learned, just against the "proof" that someone with ADHD has - and not because of ADHD specifically, but because generally speaking any argument which relies on "my experience proves X about humans" is likely to be short-sighted.)