I'd think that the odds are relatively high in favor of him exceeding the benchmark in this case.
Barring any LD issues that you don't yet know about, I mean.
I'd think that it'd be well evident by late Kindy whether or not he seems to be exhibiting any other signs, or if the peers seem to be catching up to him, etc.
I'm trying to think about the other kids I've known that devoured those MTH books in preK and Kindy.... I know of only a handful of them, and all of those kids have since been identified as GT. My DD (PG) was the only one that had 'aged out' of the books by kindergarten age, though most of them had by the end of 2nd grade when more NT/average learners like them best.
Don't know if that means anything, as it is anecdotal, obviously-- but that kind of comprehension and interest is remarkable, I think, even if the strict decoding part of it may not be.
