I've actually known a few savants. One was perfectly normal boy, but could do calendar functions. You could give him a date, and he would tell you what day of the week it was. If he was alive on that day, he could tell you the weather. He lost the ability in puberty (or decided to quit telling people about it)
A friend of the ex wife was a caregiver in a halfway house for adult retarded men. They had a severely impaired indivdual who was a calculator. He was an adult and could out calculate anyone with a calculator.
That's a different phenomenon ... the autistic folks generally have (extreme) difficulty 'reading' other peoples' emotional states, controlling their own, and understanding the fuzzy issues surrounding social interaction. And memorization, again, doesn't necessarily translate to understanding in their case. Imagine an 8 year old repeating, verbatim, a dirty joke that he heard someone else tell, and laughing uproariously about it. When questioned, he hasn't a clue what it means, or why it's funny, or why it's inappropriate to tell to his grandmother ...