It is very difficult to explain in one short answer what autism is because it is unique to each person. I disagree that all autism is caused by toxins and vaccines. I know there is a class of autism caused by damage from toxins, but that is not the case with my son. BTW, a good diet will make anyone feel better, autistic or not.
My son has High Functioning Autism or Asperger Syndrome and it is obvious that it is genetic. He acts just like my husband, my BIL and FIL, my husbands brother and father. The only difference being that my FIL and BIL have worse symptoms than my husband and son. Also, my son started speaking quite young and never lost the ability to speak. It is clear that his condition was present from birth, before he was ever introduced to dairy or gluten or toxins. He was on an optimal diet of close to 100 percent organic foods, no dairy, no wheat, no sugar, and something was still amiss.
There is a lot of information out there about autism. I think the best way to figure it out without seeing a doctor would be to read a book about Autism Spectrum Disorders, maybe one specifically about adults.
My husband and his brother were both considered slow when they were children. It is a label that was used at that time because people had no other way to explain it, not that they really may have been slow. They both received speech therapy and still have issues with misunderstanding people in conversations and having a hard time getting their point across.
Here is a great article I recently found by an adult with autism or Asperger Syndrome
Good luck! If anything, I hope your husband can start feeling better. I know with my husband and son, being sick turns our home upside down because they have trouble expressing themselves.
P.s. Not trying to start an autism argument here. Just letting you know that there are many different opinions out there about autism.