Yes, it is a coincidence. My son is autistic. I postponed his vaccinations because of other health issues not related to his autism. His pediatrician recognized his autism associated delays 5 minutes before his first vaccination.
Autism is becoming better diagnosed. Children who, in the past, would have been described as "difficult", "weird", or "retarded" are now being diagnosed with Aspergers, which is in the autism spectrum.
I suspect that another reason for the increase in autism might have something to do with chemicals we might be putting in our water, food, or air. What do you think?