No case there at all. The guy who reported it merely relayed factual information. I don't even see where the information could even be remotely considered secret.
I don't see how that would be necessary under the law of most states. The only question is whether he knew that it would affect the contract between them, and he had no privilege to interfere.
My guess is that it was his intent to interfere. The best defense would probably be that he had a privilege, but if Allstate is held to have violated this guy's rights, I don't see how any privilege would apply.