At least in Mississippi, if they want to go to executive session they have to declare so publicly during the regular meeting and cite specific reasons (matters dealing with specific workers, legal matters that require confidentiality or about the city's exposure, etc.). I think they typically go to executive session if they decide they need to fire an individual. But, those are the only matters they can discuss. Anything outside that and they are required to return to a regular (public) meeting.When I was on a school board, the board could go into what was called "executive session" where everyone was out of the room except the school board and the school superintendent. I would think that if their situation was that they were in an "executive session," it is NOT considered a public meeting, and if that were the case here, the recording might very well be illegal.
Now, if this occurred AFTER the meeting was done and deemed as closed, they were still in a public place and the recording might be legitimate, although I thought that such recordings in Oklahoma required at least one participant to know of the recording. But, with the reporter out of the room and his recorder in the room, that one is questionable.
i think there will be more that comes out about this. It will only take one participant to decide to come clean and share about all the matters discussed outside of the public view.