In this case, they were found not guilty of the rape. That does not mean they were not guilty of the attack, which was one of a series of violent incidents that occurred in the park that night involving a group of youths. At least one confessed to the attack, and admitted to groping the victim, but not raping her.
It’s still not strange that people confess to crimes they didn’t commit. It happens far more often that most people realize. My statement was not presented to assess the innocent or guilt of these boys in this particular crime. 8>)