[EdHominem]

It's not non-public information, it's non-public insider information, upon which you cannot legally trade.

"illegal insider trading requires that you not only trade on the basis of important nonpublic information but that you also have some sort of duty to keep the information confidential." - Kiplinger

If you overhear insiders talking, you can trade on it. (Unless you're in a position where they have reason to expect that you cannot, such as if you're an employee, etc.)