The WASI is a screening instrument, with as few as two subtests. It may be that they happened to be the two strongest skill areas for that child, and when the comprehensive assessment was done, the overall score now drowns out the areas of strength with other areas that are not as strong. How long apart were the tests given, and did the child have a range of scores on the SB5, or were the scores reasonably uniform?

...pronounced like the long vowel and first letter of the alphabet...