Your DS sounds mathematically talented to me but that does not necessarily mean he'd score above 130 (or whatever the cutoff number may be) on standard IQ measures. I assume he was very young when he was tested. If he didn't feel comfortable being in a room with a stranger, he might not done as well as he could have.
Did the school not offer you an option to go over his assessment results in person? If they didn't, maybe you still could ask for a meeting because you have some concerns.
A small school that is willing to offer individualized instruction might be a better fit for your DS than a sought-after gifted school that has a long waiting list. Some elementary school teachers, including those who teach at gifted schools, may not feel comfortable teaching math beyond 5th grade level. My first choice for my number-obsessed child was to send her to a public charter school where she would have had an access to their high school faculty even as an elementary school student. If your state offers a similar setting, I'd certainly look into it.
