FWIW, the NNAT is largely similar to the Matrix Reasoning task of the WISC-IV or the Nonverbal Fluid Reasoning task of the SB-5 or the various Raven's tests.
So, would you consider the Raven or NNAT to be an IQ test if they are only testing what would be one piece of one subtest on the WISC or SB? Can you assume that a child who tests in the 99th percentile on the NNAT or Raven is going to have a gifted IQ or that a child who tests more poorly on one of these tests isn't gifted (assuming accurate measurement, of course)?
