I'm not sure why those "some states" are more important to the conversation than the ones that don't have such laws.. Such a law makes sense when the perpetrator can just claim the victim lied about their age. In this case we have actual evidence of them doing so though.
And why are we talking legal aspects anyway when the whole thing started as a moral problem? They went on twitter and contacted his friends and colleagues to accuse him and for everyone to shun him, not the police to get him arrested.
They are important because most of the country doesn't even allow a mistake-of-age defense, and if they do; there are several hoops you even need to jump through to establish that defense.
And it's still a goddamn moral problem because you're using your position, in a situation that is known for having fans of all ages, to potentially solicit a sexual situation and the main vindication will only be "oh, they said they were legal, so sounds legit." Like come the fuck on