That is a very ungenerous/unkind position that many folks take when they don't know WTF they are talking about.
Abnormalities in a kid do not instantly indicate a disorder. Yet doctors are quick to prescribe adderall to the first person that comes in their office and claims they have "trouble concentrating".
There are specific, medical criteria which need to be met for a diagnosis, and these criteria are outlined in the DSM V [1]. These are the details on how the disorders are classified, since you asked.
[1] https://en.wikipedia.org/wiki/DSM-5#Neurodevelopmental_disor...