If a provider is telling you there are no signs of autism, and yet the child has a language delay (in terms of functional communication, it sounds like) and hand flapping/jumping, then I would definitely take their statement with a grain of salt and seek an opinion from an ASD diagnostician because those are all present in ASD. It's very true that lack of consistent, appropriate eye contact is almost always present in ASD, but what is considered appropriate, consistent eye contact can be difficult to gauge, and of course, there are outliers. Being social also doesn't exclude someone from an ASD diagnosis, it's more in HOW they're social, if you will. Autism assessment is my career--at my center, we casually refer to it as "boy autism" versus "girl autism." They tend to present differently, for a myriad of reasons, and often girls go undiagnosed because they are "social."
At the very least, I'd see how he does on an MCHAT or an SRS.
