I know of children that are hyperlexic and gifted as well as some that are cognitively delayed. I think you would need to look at a many aspects of cognition and talent to determine whether one was gifted. Also keep in mind that IQ tests can be very fluid at a young age. Even if your son did not test as gifted at 2.5 years does not mean that he might never develop the aptitude in the areas that would qualify him as gifted. And yes - language issues might affect testing/assessment.