Yeah, having worked with many mentally ill folks, I feel this is a pretty common thing. It's a lot to do with the stigma attached to the phrases. If you have depression, that's a disorder too... anywhere on the spectrum? Disorder. It's a word to indicate that you have a condition that affects your everyday life - where you take it from there is, of course, largely up to you.
I am not a professional psychologist or therapist. My son has been diagnosed as an Aspergers - which is in the DSM. I know it's a term that's no longer recognised, but Aspergers describes a specific set of behaviours associated with Higher Functioning Autism (HFA). I have had a number of guesses confirmed about Aspergers kids by asking their parents and then sharing knowledge.
What's interesting for me is that quite a few people in IT that I have worked with have symptoms that are very Aspergers like. It can come down to an individual's interpretation as to whether or not their condition is a mental disorder. Most of these IT people that are Aspergers like would almost certainly reject the notion of them being Aspergers, even if you explained the behaviours.
The consensus is that we are all on the spectrum - it's just the degree that our symptoms are prevalent. For example, sleep deprivation can trigger similar symptoms, so can over-stimulation. For example, have someone yell in your ear for 5 minutes and you will exhibit some of the physical behaviours that autistic children do.
