Um - no you're not. I had this problem with ds1's first nursery. He NEVER brought home any paintings (had no idea he was auti then) because there were pore children than painting spots so the children had to push thier way in. He had no idea how to do that so never did anything. When I asked to see the notes they kept on the children they had written things like "A aproached the painting and watched- he reached out to touch the paints then pulled his had away- he watched for a bit longer then walked off. Conclusion A has not interest in painting" WTF????
Also they used to leave him sitting on a chair by himself after lunch waiting to be picked up (because they could- he would just sit there and it was easier for them) and would take all the other children next door to play (second time I saw that we removed him).
Comparing with the nursery we use now it's completely different. All the children do all the activities (at different times) and it is organised so that is a possibility.
I would worry less about him playing by himself- you may just see a snapshot there- and it is better for everyone that time is spent with children who may otherwise be disruptive. Have a word with them about the painting though.