I don't think it's a generally thing that ADHD is considered NT here. Depends on the person.
The home page here says "Wrong Planet is the web community designed for individuals (and parents / professionals of those) with Autism, Asperger's Syndrome, ADHD, PDDs, and other neurological differences.". So, it specifically includes ADHD in who this place if for. In fact, I first found this looking for stuff related to ADHD on the web.
I think a combination of two things makes some people think of ADHD as NT.
First, there's different viewpoints of how ADHD relates to autism. Some think it's related, perhaps a milder form. Some think it's something different. Some think it's sometimes a mild form of autism and/or undiagnosed autism, but sometimes something different, separate.
There's also different ways of understanding what an NT is. Is an NT someone who's, well, neurotypical, who's brain works like most peoples? or is an NT anyone doesn't have autistic traits? Or anyone without an autistic disorder?
So, those who see ADHD as totally separate from the autism spectrum, and who use NT to mean some form of "not autistic", for them, ADHD = NT.
Also, those who don't know much about ADHD aren't going to understand that it's really a different way of thinking than normal, not just an inability to pay attention. If someone thinks that the only difference from normal that ADHD people have is poor attention, they are going to consider people with ADHD to be NTs.
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not aspie, not NT, somewhere in between
Aspie Quiz: 110 Aspie, 103 Neurotypical.
Used to be more autistic than I am now.