I saw this article today, it sounds like he either uses memory techniques or his brain naturally creates imagery.
Interesting quote from the article:
Richards speaks no Spanish and started memorizing the language’s Scrabble word list a year ago, his friend Liz Fagerlund -– a New Zealand Scrabble official -– told The Associated Press.
“He can’t understand why other people can’t just do the same thing,” she said. “He can look at a block of words together and once they go into his brain as a picture he can just recall that very easily.”