I can't really say normally, as I don't have enough data (not enough cases) to say what is usual in hyperlexic kids. NT kids generally speaking (no LDs or other educationally-relevant disabilities) do about the same on the pictorial and text-based CogAT, by definition (they are the basis of the norms and percentiles). The pictorial test is used in the primary years because of the wide range of reading levels obtained in the non-disabled population in that age group, so that reasoning/learning aptitude and decoding skills are not confounded. By the end of third grade, the majority of children can read fluently. The WISC-V VCI has negligible visuals (none for children who are at least average in intelligence), relying entirely on oral verbal ability. A small amount of receptive language is required (comprehension of single words--one at a time for Vocabulary, and two at a time for Similarities), and a moderate amount of expressive language (to provide the responses; it is possible to obtain maximum scores using only single word responses, though most children use phrases or sentences).
Out-of-level achievement testing usually compares examinees to the standard norm group. So your DC's ITBS scores compare him to children on the average a year older and a grade more experienced. His CogAT should have been calculated on age-norms, using his chronological age peers. They do typically have age norms that extend a bit beyond the typical age range. I don't believe I've seen them more than a year out, though.
Is it still hyperlexia? Depends on which definition of hyperlexia we are using. Listening comprehension is also not the same as reading comprehension, even though both involve language comprehension. I've seen plenty of students who can do one but not the other (both directions).
Quantitative reasoning, like verbal, doesn't actually measure any math skills, just problem-solving related to mathematical thinking. A few possibilities: he may have had difficulty interpreting the questions, been uncomfortable/unfamiliar with the testing procedures, etc.
