The guy is not even alleged to have done anything other than exposing his genitals at any point.
I don't think this is socially acceptable behavior in 'normal' society. And in response to his deciding to visibly 'rub one off' (as I believe this term is what results in auto-flagging) towards his neighbor, his response is that she was a "trigger" for him. So he himself is already claiming that he can't control himself, which is more less the entire point of such registries. Imagine you have daughters, let alone a wife. Would you want to live across the street from such a person?
And again I'd emphasize he actually got removed from the registry. So imagine the sort of behavior required to stay on one. It's damn sure not just urinating in public or whatever.
[1] - https://news.ycombinator.com/item?id=47048094