Nothing seems to stand out to me as AS. Early reading does not indicate AS. He may just be gifted, or even poissibly, one explanation is hyperlexia. Playing parallel at that age isn't that odd. Sometimes kids may just be more comfortable playing alone as they are playing with a group. The writing thing.... could be a boy thing. My DD never had to be taught how to hold a pencil etc. and could write like crazy at a young age. My son, totally opposite. Still working on handwriting at almost 6!
Good for you for researching and be thankful you have a doc that is alert, but that doesn't mean you have reason to worry. With so many kids being diagnosed on the spectrum now-a-days, or so it seems, peds. may be more willing to investigate the possibility than to dismiss any concerns.
