Hi Willmouse, goodness me, not something anyone expects at a parent's evening!! There you are, expecting a bit of conversation about numbers, drawings, writing...and they come out with that!
I'm an adult on the autistic spectrum (Asperger syndrome), as are several others of the lovely mums on here, which might give you a clue that it's rarely a disaster these days with the right help, support and patience for/with a child (and help and support for their parents too).
Does he have it? That's the big question. They're doing the right thing by asking their Ed Psych, but you might want to then ask your GP to refer you to a developmental paediatrician, as those are the people who actually do a proper diagnosis or discounting of this theory, rather than a "what might the school need" sort of thing.
From what you write, I can see why the school may have thought "aha!" (though I still think they could have chosen a more suitable moment...). Many children with an ASD are not really badly behaved, but are over-precise, 'little professors', socially awkward, very neat or obsessive about routines or hygiene or having things a certain way. Maybe not very good at sport or fine motor skills. They maybe don't like unexpected change, or can't understand emotions or body language or face expressions unless someone explains it in words. They're just as likely to be quiet and reserved, preferring to withdraw rather than create a fuss, not happy in big noisy parties or unexpected events.
Often our senses are hypersensitive or work differently to yours, so we find noises immensely loud, lights immensely bright, odours immensely overwhelming, the texture of clothes unbearably scratchy or tight, etc. Or can seem entirely deaf if people speak to us, because our brains usually can't concentrate on speech if we're looking at something, so you have to get our attention first.
But it's the ones with behaviour problems or almost total lack of speech or very low IQ that the public remembers (about 1 in 7 of us, I read this week), which is why autism has had a 'bad reputation' with a lot of the public . Instead of helping and understanding and respecting us no matter where we are on the Spectrum, too often people just fear us because of this misunderstanding about what we can be like and why. I think this is why it's such a shock for parents, because they imagine that every child will be a nightmare of behaviour all through their life and always unable to look after themselves, rather than be like some of us parents on here. Some individuals are low-functioning or very badly affected, of course, which is why I try to help get much better help for the parents and the children concerned.
As Shells says, the best thing is that he may get some extra help to try to understand the world, and you'll understand him better too. And if it's not an ASD and this is just him being him, the outcome will be that you've learned a bit about the 1 in 100 of us who are on the Spectrum, which is always interesting .
Keep asking...loads of good people here to help.