I can't speak for US law. But i worked at a company that had something similar happen to them. We went to the police and they said there's nothing they can do.

The guy that 'extorted' us dropped out of law school and knew exactly what he could and couldn't say.

So the answer to that is probably that it's not extortion if you know your way around the law and are clever about it. He never extorted us, he just offered to sell us the domain name that was shit talking our company. Of course he's allowed to SEO the domain name with a link farm, that's not illegal. And it's not slander if it's true or not presented as a fact, just as speculation.