Hey C., My oldest child is 18, and while all children are different, one thing I think most parents and doctors will agree on - kids go through eating phases. Especially toddlers. Your son has been exposed to some wonderful eating habits so far, you should really be proud of that. I don't think you have anything to worry about. Keep in mind that toddlers are also finding some independance and will refuse to eat something just because you want to them to eat it. Continue to offer those veggies and introduce new ones (as always watch for food allergies and new favorites). Toddlers will often go through phases where they will want to eat the same food for breakfast, lunch, and dinner...for a week...then not eat it again for months. Just be happy it's not chicken nuggets and fries!
I really don't think this is connected to weaning at all...I think he is just expressing himself, and let's face it, how many ways do kids that age get to do that? And it is really not worth fighting with him to get him to eat things that make him truly unhappy, even if he liked them a week ago.
Take a break and bring back those old favorites in a month and see how it goes. Honestly, he may decide he does not really like all of them, but you never know. I always try to lead by example and tell my son it's okay not to like it, but it's not okay not to try it.
Good luck to you!