[borski]

You’re right; this fact alone does not diagnose someone with ADHD. Nobody is disputing that.

But we don’t have the parent’s full context - they may have had a dozen other symptoms that they have finally been made aware of, and in that context this may be a symptom.

I don’t play video games enough for it to be one for me, but if I did, I would almost certainly have trouble being a “completionist.” That doesn’t mean I have ADHD, but coupled with about two dozen other personality traits and symptoms, and tons of self-reflection and medical help, it could be a part of that.