Will our little white lie about a reason for termination come back to haunt us?

Q: “We mutually agreed when ‘John’ left the company to tell any prospective employers that he left because his assignment ended. However, since we operate in a small community, I found out that some of my staff had unofficially told their friends at another company that John was fired. This resulted in him getting terminated at this company because they said he lied on his application about never being fired before. He tried to explain, but we’re in an at-will state and the company officials said there’s nothing to discuss. John is now threatening to get a lawyer and take us to court for violating his separation agreement. Are we in trouble for revealing that his departure from the company was not entirely voluntary on his part?” – Anonymous, Washington