No, it's a measure of how well you perform on the subjects tested by the SAT. There are many things that correlate with high SAT scores (e.g., grades, being Asian?), but it is definitely true that you can prep for the SAT without any meaningful amount of money. I don't believe that anybody has ever alleged that SAT scores are a proxy for intelligence, though I suspect there is a decent correlation. In my mind it is a useful, objective, universal measure of how an individual student is able to prepare for and execute on a difficult task.