This morning, I had the need to unlist several events to keep them from view while I made changes in the posts. I noticed that the events were unlisted for my regular users but for the same users, the events were visible and accessible via the Upcoming Events calendar.
This is a self-hosted instance with a recent update (several weeks ago).
This isn’t completely unexpected (though I can see why it’s confusing), when a topic is unlisted the content is still reachable if you visit the URL directly, even by regular users… all unlisting does is literally remove the topic from the topic list. We’d have to add some additional logic to also unlist an event when a topic is unlisted.
In the meantime, if you want to hide a topic and the event from regular users while editing you could do so by moving it to a category that regular users don’t have access to.