If I remember right, something like under 90k earned by the student's family, they pay nothing. I haven't worked there in 2 years, so the math is a bit fuzzy but the concepts are accurate.
as another comment points out, some of the salary and wage spend could be considered part of 'financial aid.'
That is only undergraduate aid applied directly to tuition. Per Note 12 on page 43, "Total scholarships and other student awards" was $613,243k, of which $457,639K was in direct credits to expenses.
That said, I don't know where the GP got the idea that most of the endowment is earmarked for financial aid. Per page 11, that earmark is specifically 19%.