Forgive Steven, he has a very low verbal IQ. [...] He just takes everything you say literally.
The author seems to be avoiding mentioning autism, but since they're trying to reduce someone's likelihood to interpret things literally as a function of IQ scores the author ends up stil referencing autism, just misrepresenting it.
It is common for autistic people to have a relatively high verbal IQ and relatively low non-verbal IQ, yet still have a tendency to interpret things literally. The cause isn't IQ at all, it's autism.