I usually describe the test as a measure of knowledge of social conventions, which has some overlap with social reasoning skills, but doesn't necessarily translate to strong social performance, especially on the fly. Being able to articulate what people usually do or think is not the same as being able to read actual people or navigate live social situations. It's a bit like being an anthropologist or animal behaviorist, studying the behavioral patterns of a population from the outside.
It is also highly culturally-laden, with assumptions/values relating to market economies, representative government, and other predominantly Anglo-American concepts.
What it has to do with intellectual ability is very similar to what vocabulary and information tasks have to do with intellect: a high cognitive person living in a certain environment is likely to acquire more of this type of knowledge than a lower cognitive person. It is a measure that correlates well psychometrically with intelligence, even though it is not so much a measure of "innate" reasoning ability.
