My understanding is councillors who are not members of the committee could attend a meeting of the committee, just as members of the public could, and could speak in the public part, but would not have a right to remain if the meeting went into confidential session.
Does this mean that during such a meeting, the conduct of the councillor would not be covered by the code of conduct? IMO, not necessarily. The councillor may only have the rights of participation of a member of the public at the meeting, but they are still councillors. It would depend on their conduct and the context of it. Ultimately, it would be up to a Monitoring Officer to decide.