He said there are significant auditory processing issues that come into play and that he "over thought" his answers and ended up getting several wrong because of giving too detailed of an answer (how are green and red the same? Answer they wanted - both are colors. My son? Both are on the light spectrum, blah, blah, blah). But that answer is wrong on the IQ test.
The test results are invalid due to the neuropsych's obvious lack of expertise in testing gifted children. The discrepancy with prior testing is no mystery, regardless of the accuracy of those prior results.