Being a piss and ASD

A few weeks ago, my 3.5 year old had an assessment with a pediatric neurologist to determine if he had some for of autism or behavior disorder. Of course, my boy wasn't having anything to do with this new doctor and his activities. He ignored every attempt to get his attention, he used hand gestures to answer questions, and sat sullen in my lap. Somehow the Dr made an assessment.
He said," if anyone questions him or you, tell them you've seen a neurologist and to mind their own business. He's not autistic, he has no behavior disorders. He's a cute kid and extremely smart, but he's a piss. And what do we do with pissers? We give them choices. He can choose to speak or choose to follow directions or he gets nothing. He's stubborn. Just be consistent with him and he will outgrow it."
A- I didn't take offense because he spoke plainly and I liked the honest raw truth. I actually laughed at his statement. B- Wed been doing the whole choice and consequence thing.
  I left feeling disheartened because he was my last hope to figure out what was wrong with this kid of mine. We'd been around in circles and no one could tell me why he is how he is. I have worked with many many young children and I know the difference between a child who is stubborn, and a child who can't cope in social situations. I did schedule a follow up per the Dr's request and hoped that our next appointment would be different.

A couple days ago, we had the follow up appointment. The Dr asked me how it was going with his behavior, but this time I had written down specific examples of the things that concerned me. After sharing those examples, the Dr did another assessment. He got the same results, but more defiance than before. It confused me because on the drive there, my son had said he was ready to talk and play at the office and now he was giving the Dr the cold shoulder.
The Dr decided to diagnose him with ASD- autism spectrum disorder. He said he uses the term lightly because he can't evaluate where my son would be on the spectrum, and also he doesn't like the unsure term( he's more of a either you are or you aren't kind of guy). However he knew in order for us to get insurance approval, we'd need a medical diagnosis. He gave a referral for an ABA therapy assessment that can determine what areas he needs help in.
Even though I felt a weight come off me because I knew we were finally getting the help I knew he needed, I realized that our battle has just begun. We'd fought with the school district and private speech therapy and insurance to get some help. Now we have someone that listened and we get to battle more.
It's worth it though. I long for the day when I can understand his behavior and needs and not have to guess what he wants. I can't wait to see him open his mouth to speak to his friends and to participate in school activities. I hope that whatever is holding him back can be changed so that he can learn to cope with his emotional outbursts and social life.
One step at a time. Deep breaths.