I don't know anything about autism, and my kids both had their vaccinations with no problems, but I do have some experience with thimerosol. I reacted badly to it the first time I put in my contact lenses many years ago. Seems that preservative caused my eyes to get so bloodshot that I had to return to the doctor. My reaction necessitated an immediate change in solutions. The doctor told me that something like 20% of people couldn't use the solution for the same reason--sensitivity to the preservative. That was around 30 years ago. Now the cleaning/storage/drops aren't made with that preservative very often. And, it's not uncommon to find it listed on the box "contains no thimerosol" (or at least that used to be the case. I no longer wear contact lenses.)
While it does sound extreme to me, because of my reaction to thimerosol in contact lense use, it isn't too much a stretch for me to believe that there COULD be people who are more sensitive than I am who could have a worse reaction. If my eyes became extremely bloodshot and painful with simple solution use, perhaps some poor child reacted badly with an inflamation of the brain causing autism--due to being injected. Understand--I do support vaccinations--but it's the thimerosol use that could persuade me that there is a real possibility of a reaction.
Sorry about your experience with the drug. There are reactions to every medicine, no matter how ordinary. I feel sorry for these parents, desperate for some solace in knowing why the autism occurred, and also falling victim to lawyers' greed.