My ds has recently been diagnosed with High Functioning Autism. A couple of people with dc who I was friendly with suddenly melted away when I told them he was being assessed - before he was even diagnosed. He is not aggressive, just a bit quirky and it didn't seem to be a problem till I openly said he was being assessed.
I know the general consensus on here will be that it would not bother you if your friends child was autistic but this has not been my experience so far in rl.