Side note: the "prior accusations" in question were because he jokingly exposed himself to a classmate in class, BTW.
Because it's not like there's a difference between that and rape or anything.
ETA: What it comes down to is that this kid would have been getting ten years in jail on a "statuatory rape" charge for having consensual sex with someone three years his junior.
For those of you who are unaware, statuatory rape charges between consenting teenagers are unevenly enforced when it comes to race -- most of the convictions coming when the younger teenager is a white girl and the older one is a non-white male. You want to debate why that is, go ahead.