I suspect a lot of this is variance on surveying methods. I could see "Literacy" be defined anywhere from "able to read the survey enough to pick out where to mark "yes/no" and "sign here"" to "Able to read YA novels", and in the US it could well be "English literacy" versus "Any literacy". I knew plenty of kids growing up who had grandparents living with them that could read Mandarin or Spanish just fine, but who had pretty limited English skills.