Could be. There's a lot of funding for scholarships that can be allotted in various ways, based on the admissions committee's discretion.
I know quite a few get offered partial tuition merit scholarships. Perhaps more than four end up with full tuition. But there is a program offering exactly four full-tuition scholarships each year. And the four recipients get announced here.
Yeah, can confirm that there are other scholarships -- I got the "distinguished student scholarship." WashU is insanely generous.