I believe that a likely explanation is that Lefties are forced from a young age to adapt to items and technology that simply stated, does not make sense. Scissors, Can Openers, learning to write, the list goes on. As Lefties are forced to adapt their learning to a different method than other people (as very few people can teach using their off hand), by the time a lefty has reached adulthood, they have completed a far greater amount of problem solving in their lifetime, making them more skilled and appearing to be naturally more intelligent.
