Lucca luckily for me I didn't have much to do with "the spectrum" before I retired for which I am grateful as it seems like a minefield.
However, my thoughts on "oh he's/ she's" ??? are often - not always - but often used as excuses.
An excuse for not wanting to see "what's real, what's not real and how to tell the difference" Granny Weatherwax courtesy of Sir Terry Pratchett.
It would appear that IF things are seen, too often they are seen, then assigned to "Someone" - that's not him/her/the parents- to fix. May be I'm just getting cynical in my old age.
In this world of "Rights" too often the balance of Responsibility is ignored. Either because the knowledge of Rights AND Responsibility isn't learned or there is very little (no) interest in knowing that for balance both those R's need to be used.
We all have bits that need work, firstly by our parents, family, teachers and friends (I believe in the saying it takes a village to raise a child) and then it's up to us to when we are adults to get ourselves fit for our roles in society.
So in answer to your question of "oh he's" on the spectrum. May be they are and in that case he/she needs help to find ways to live in the world in a way that is OK enough for them and OK enough for we "others" who are around them.
I really dislike it when it's an excuse for any rude behaviour.
It is really up to the person in the situation to discern if another persons "rude' behaviour is and within their ability, or not, to manage their behaviour due to any unchangeable conditions?
Or is the "oh he's" ... a way of giving permission for unsociable behaviour, an excuse to make no changes?
I don't really know but I think when we are in those situations often with the same people we can sort it out.
If it's a stranger in passing it's much harder to say if that person is on "the spectrum" or if it's an excuse.
However, I have a friend who works with people on "the spectrum", where she works some staff to put on kevlar protective clothing. I am not exaggerating, body armer and protective sleeves so "the spectrum" is very large.
We used to teach together and now she works in this very specialised area and she loves it. She tells me with the residents she works with there are no excuses, no political games, they are who they are and they are how they are and you can either deal with it or you don't work there.
If your gut is telling you the "oh he's" an excuse you are probably right but ... proceed with caution :-)