Sounds to me like hes just anti social
I don't know what to say. It may not have to do with parenting issues though. He could be shy or introverted. I will clam up and observe people if they aren't talking about something I feel like I can talk about....
For instance in high school if a group of girls are talking about their relationships with their boyfriends, I'll listen to them, but I likely won't contribute... If I find the conversation too dull, then I'll open my sketchbook and start drawing or find something else to do.
If people are talking about something, I may try to join in, but very seldom do I seem to do it the right way... I tend to interrupt... My timing is out of sync with the group. Try as I may I almost always seem to start talking just as someone else is, even if I sensed a pause. If they get over that and let me speak, I may join the conversation (with the tendency to dominate if I don't catch myself)... But if they don't or I perceive they are not interested, then I will clam up again and slink back to my original spot and go into "observation mode" if I still find their conversation worth listening. If not, I may slink away and retreat into my own mental world and tune them out to a degree.
Sounds like a problem with Parenting skills, and the Mother has a Parent/child interaction difficulty, ask her why she thinks he has the Behavior considered Autistic, on reading your short Post about her son, he sounds like a Normal Boy, perhaps some classes or counciling for his Mom would be a good thing.