Why would they issue a statement saying that he was going to stay on without some form of assurance from him?
I mean, you're writing a release stating that you're firing your CEO and accusing him of lack of candor. Not exactly the best news to give. You're chasing that with "oh by the way, the chairman of the board is stepping down too", so the news are going from bad to worse. The last thing you want is to claim that said chairman of the board is staying as an employee to have him quit hours later. I find it hard to believe that they'd make mistake as dumb as announcing Greg was staying without some sort of assurance from him, knowing that Greg was Sam's ally.
Maybe to make it clear that if he leaves, it is him quitting not him being fired. This would avoid potential legal issues.
Maybe they thought there was a chance be would stay.