Dylsexia is not a problem of seeing numbers/letters backward or out of position. It is a language based reading disorder that is a result of a poor phonological system. Often dyslexics show reversals, not because of a faulty visual system, but because of difficulties in processing, sequencing etc. While the reversals can be a red flag, it is only one symptom. And yes, some of your son's reading scores are fine - but he shows some vulnerabilities that indicate there may be a problem that is masked due to his intellect.
You are noticing issues around reading. He is noticing the same. He has some very weak scores in comparison to his stellar intellect.
Follow your instincts - yes you need to get a second opinion. His rapid naming scores are quite low - This is a HUGE red flag. Your instincts (and mine) could be wrong - and I hope that they are. But, I would press to get more information.
Here's another website that you may find helpful:
http://www.childrenofthecode.org/
