My D (now 15) was very much a "parallel play" kid at that age. In fact, when she went for her kindergarten evaluation at the private school my older D attended, the person commented that she had done nicely, but hadn't actually spoken to any other child the whole time she was there. I have to say, D did have some behavior issues at that age (liked to "stir the pot", I would say). Maybe partly because of boredom, but also sometimes a lack of social skills on her part.
She was diagnosed with a non-verbal learning disorder a couple of years ago. She did eventually find friends at school (really not until about 4th grade, though). They are not really at her level intellectually in a lot of areas, but they get along well as a group.
I know what mycupoftea is saying about knowing too much. Far too many conversations between D and other kids started with, "Oh, you like Harry Potter, too?". Then D would bowl them over with her intricate (almost verbatim) knowledge of all things HP. And then D would be disappointed when the other kid's knowledge was fairly superficial.
