Unintentional long post:
In nursery DS is a completely different boy. I've seen it in action. At home/outside of nursery 180degrees about turn.
In Nursery - doesn't interact with the kids. Doesn't want to do anything, other than sit in the book section - without books. Doesn't want to paint/play/read, unless told to go there. He has to be told what to do, and then will stay there doing that. Didn't used to feed himself. Basically the nursery think there is an autistic streak.
But outside of nursery he will do anything he wants. Babbles continuously, decides when and what to play with, demands whenever he wants, feeds himself, even sometimes wants to make his own food (like taking out a pizza from the freezer and putting it straight into the oven - I was there!!). Pours his own drinks from the fridge. Plays from one thing, to another etc. You get the gist. He plays with other children - though perhaps not on a completely free style as others might.
Now when I watched him in nursery - to me he looked completely bored and looked like he was "killing time", waiting to get out. But the nursery took offence at the idea a child could be bored in their place, and said I was in denial.
Now the only time he seems to enjoy nursery is on trips outside - even they admit he likes it and is quite lively, and if the nursery, for example, is having a party.
The other factor is his speech is not clear. I can understand him and family can about 60%. But I notice in nursery they don't, and they don't seem to try - they guess and move on. I also notice that when he realises someone can't understand him, he either clams up or tries an alternative word - if he knows one.
Given his behaviour outside of there, I doubt he has something wrong, but is there anyone else out there experiencing a similar situation.