He's been in nursery for 7 months now. Staff say he's quiet and they have to encourage him to participate in activities (and then he does, and he enjoys it) they say it might be he is less confident. They get surprised when he is chatty in the nursery!
It might just be in his nature that he’s different in a busy, noisy environment. If he generally seems happy to be dropped off at nursery then it probably doesn’t signal an issue.
Maybe he was just a bit tired, or behaving differently because you were there? Did you ask the staff whether he’s normally like that while he’s there? How long has he been there?