If the MMR vaccine has never contained mercury, why is it called the autism vaccine?

Is there something else in it that has been linked to autism? I heard something about vaccine-induced measles virus being found in the brain and intestines of a 9 year-old autistic boy.

I only want answers from people who know why MMR is attributed to autism, not from people who deny it. That’s not because I don’t want to listen to reason. It’s just that I know that side already and am just interested in why MMR is linked to autism when it never had thimerisol.