It sounds as though your parish council has overstepped the mark here, unless there are provisions within your standing orders for this. Parish Councils must conduct their affairs in public, so the nearest we get to a secret meeting is the consideration of confidential items in closed session. In order for this to happen, the item must appear on the agenda of a meeting of the council or a properly-constituted committee at which it is to be considered. It must then comply with the very limited list of conditions for the exclusion of the press and public. A resolution is required, setting out the circumstances and the reasons why the item must be discussed in closed session. All of this must be recorded in the minutes of the meeting. If none of this happened, the council has not made a legal decision.
You haven't given the nature of the allegations, but am I correct in assuming that this was, in effect, a complaint against the council?