Well yes, in the larger sense, dyslexia is entirely a culture-specific phenomenon. Our brains did not evolve for reading -- it is an extremely recent cultural invention. It should be no surprise that brains are imperfectly adapted to this artificial activity, and that some brains aren't very good at it. There is nothing "wrong" with those brains in a biological sense, and before the invention of literacy there would have been no conception of them having a "disability."