Also from http://www.autism.org/savant.html
The reason why some autistic individuals have savant abilities is not known. There are many theories, but there is no evidence to support any of them. For example, Dr. Rimland speculates that these individuals have incredible concentration abilities and can focus their complete attention to a specific area of interest. Admittedly, researchers in psychology feel that we will never truly understand memory and cognition until we understand the autistic savant. "
Perhaps his autism helped him figure out all the small things to landing 3 pointers.