This is an interesting brief because it draws a logical conclusion without addressing the underlying issue. I don't think that children with autism have abnormally high mercury levels at age 7.2; as the study appears to show. This, however, has nothing whatsoever to do with whether or not the very high level of mercury in vaccines causes, or can contribute to the cause of, autism.
I could publish a study that showed that people with radiation burns suffered at age 5 have no higher radiation levels at age 40 than the average populace. That has nothing to do with how the burns were caused initially.