My view is that the question of whether the council could decide to send a press release was borderline, although the clerk being present was in a better position to judge than I am. Certainly it is correct that a substantive decision cannot be lawfully taken unless it is backed by an agenda item, previously published with proper notice.
It is reasonable for a council to discuss an important topic without notice, but the constraint on making a decision remains. However, provided there is no formal policy in place to the contrary, the council could have requested the clerk to issue a press release. The clerk is able to make decisions (in their role as proper officer) without the need for an agenda item, provided it is on a matter where the clerk is deemed to have delegated authority. But in those circumstances, the clerk would decide what to do, having listened to the council, but not being bound by the council comments where a formal decision cannot be made.
The public should only be excluded after a motion to exclude for a specific reason (such as the risk of breaching a duty of confidence) has been passed by the counciil.
Minutes of a council meeting must be kept, and must record all decisions made. Minutes should not, in general, record the debate leading to a decision. Minutes must be approved by the council - in practice this should be either at the meeting which they describe or at the next meeting. Once approved, citizens have a legal right to inspect minutes.