The entities that have access to flight manifests have far easier ways to identify who's behind your account. It's not a threat model worth seriously considering.
Internal flights in New Zealand don’t need ID. So if you knew you were going to posting your terrible flight experience, you could fly under a fake name.
Not public but definitely written down and semi permanent. It’s like leaving a trail of breadcrumbs that could eventually lead to you. In this case, it gives a determined actor a specific course of action to follow (find the manifest).