Nevertheless, you aren't alone in interpreting such bids in a negative way. I sometimes ask people, especially defense clients, straight up: "Are you a person who finds comfort in discussing times when others have faced similar problems, even if there are still a lot of differences? Or would that make you feel that you weren't being heard as an individual?"
For example, it can imply the person is saying they recognize a (typical) trait in themselves. It can also imply the person does not have a diagnosis, but does recognize themselves in the description. Or it can imply the person is interested in figuring out if they have a diagnosis. It can imply an affirmation of sympoms ('oh, now that you say it, I do recognize X or Y in your behavior). It can also be used to create common ground or sympathy. I wouldn't assume harm though (theory of mind!).
I have an ASD diagnosis and it was not a matter of a 15 minute questionnaire as suggested elsewhere in this thread with regards to ADHD. Yes, I did need to fill in a questionnaire. After that I had to wait almost a year til the diagnosis process was started. It included detailed historical analysis of a parent ('hetero anamnese'). I would like to assume all ASD diagnosis are proper, though mine was after DSM-V was introduced so I have autism but no specific label.
From what I understood, its being discussed in the scientific community AD(H)D is merely a variant of autism.
When I see a movie like Girl, Interrupted or Ik Ook Van Jou it is supposedly about a young woman with borderline (BPD) but all I see is a young woman with autism instead. That's just my personal take though.