Lots of crimes are felonies and not sexual assault. Not all registered sex offenders were even accused with sexual assault. He could be registered as a sex offender but he's not accused of any kind of sexual assault.
He's not being "let off the hook" because it's an entirely different case. The boys involved were minors at the time, and the accusation of sexual assault didn't happen until last year. And they had to serve a penalty for spreading the video around, I believe (unless it was just for the possession of the video, don't remember). The event occurred 3 years ago. Washington alleged crimes aren't related to sexual assault. It's revenge porn and possession of child porn.