Therapists are just people with an education -- which can mean a lot or absolutely nothing. Autism is also a highly variable area of research that is growing and adjusting constantly as people gain understanding.
Personally, I think the fact that there are likely very few autistic individuals in charge of research, DSM-V qualifications, and development of treatment methods points to a high probability that many in the therapeutic and psychiatric communities could be way off base.
With that, as well, comes in to play what they've been finding: some autistic individuals learn to mask incredibly quickly. I can make fantastic eye contact. I can also tell you that I taught myself how to do that. Therapists base everything on what you tell them and what they can see. If you are autistic and learned to mask quickly and learned how to interact with neurotypicals, you aren't going to seem autistic. You may not have the words to describe your internal experience (especially if you're just now realizing all of this. It's taken me years to understand and be able to relay my actual childhood experience vs what people saw as I quickly became adept at masking...special interest in psychology can do that 👍🏼) so there's no way for them to truly know how YOU experience the world around you. How you take in stimuli, how you react, and how you present are all realistically separate. As far as I'm concerned, YOU are the only one who can truly know. But that's just my two sense 🤷🏻♀️
(I've completed my undergrad for biology. I've dealt with and seen many therapists as I am diagnosed with C-PTSD. I've assisted my friends who became therapists in their studying and learning. I have learned and taught various coping mechanisms to many individuals with a wide array of diagnoses. Therapists are just people with some formal training. It doesn't make their opinion an end all.)