Secret = You are the only one that knows it. Private = You and some number of people know it but you decided to share it with them. Public = I don't care who knows it.

It would be more clear if nobody was used instead of anybody but that would be a double negative.

Does that help? I think the point of that statement was to point out that privacy is not the same as secrecy and when people are attacking privacy they are equating it with privacy.