Schools like Harvard and Princeton look both for well-rounded students ("future leaders" they call them), as well as diversity in their student body. This means they won't accept, for example, 100 top violin players in the same class, no matter how impressive their individual applications are. Instead, they want a complete and balanced orchestra, for example.
So if, hypothetically, Asians tended to disproportionately cluster in the same extracurricular activities, or have less extracurricular activities, then there would be a very valid non-race-based explanation for the SAT gap.