We told ds that he has a superpowered brain which often works faster than ours, so please be patient with us mortals 
We explained having superpowered brain was called autism, and pointed out a couple of family members who have high functioning asd. We also watched the cbbc programme.
We explained that his super brain worked differently to most other people, and this was why he had a helper in school, to explain things that people with non-super brains said, or did. Also to explain how to do his work, because his work was designed for most people who had non-super brains.
He is very proud of his super powers. We occasionally mention it in reference to his asd traits too. Such as, 'oh yes, ds knows all about trains, that's because he has a superpowered brain and has spent a lot of time learning about them'. Or, 'well, your superpowered brain likes to know all about where we are going and what will happen when we get there, so we will look on the website for pictures'. If he gets frustrated at us for not understanding him we say 'please help me understand, explain it again, because my brain isn't superpowered like yours'.