Can you be autistic and sociable?

My 6 year old son has many (mild) symptoms relating to autism and has been referred by his optometrist to a paediatrician for evaluation. The vision and hearing issues he experiences are developmental delays and his optometrist has advised that it would be unusual to see his visual developmental delay symptoms outside of the autistic spectrum. However, although lots of things fit (hand flapping, tantrums, behaviours, echolalia, lack of imaginative play, clumsiness and poor co-ordination) my son is very sociable. He likes nothing more than a party and actively seeks out the company of others. He sometimes has issues fitting in with his peers, but more often than not he is fine. Also, rather than being overstimulated by external stimuli, he actually has always been understimulated, seeking out ways to stimulate himself constantly. He hates staying indoors and would always rather be out and about. I can't get my head around this as a symptom of autism or even aspergers as my understanding has always been that autism involves social withdrawal. What else could it be? I am not looking to label my child, simply to better my understanding of him and aid his development as much as I can. Your help would be much appreciated. thank you.