Spark subscribe is using your key (access token) so I think you get to see it but no one else does. I listened for that event name and didn’t see any after a few minutes.
You have to be logged in to get any of the event streams, and those streams -for you- will always include your private events as well. If you’re worried and want to test, try making another account, and subscribing with that one, and search for your private events.