Pretty bad memory!

NYU's median is 522. EVERYONE would have to have a 522 for their 10%-ile to be 521!

For the record, it's 516.
MSAR hasn't published Kaiser data yet, so I'm not sure where that comes from. Given that NYU has twice as many spots, with an MCAT that's a few points higher, your shot would probably be the same at both (around 0% with a 510, and progressively higher from there).
Also, not to nitpick, but while around 50,000 people apply every year, around 70,000 people every year take the test. So 98%-ile puts you in the top 1,400, not 1,000! The 20,000 people taking the test and not applying every year are NOT the top 2%!