Ah, okay. Thanks for clarifying.
Usually, when talking about notifications, “persistent” means “until it is explicitly removed by the user or by the sender.” https://specifications.freedesktop.org/notification-spec/notification-spec-latest.html
If you have removed the notification, well, it’s gone. Not sure why you would expect otherwise.
The media player controls widget is not a real notification. It’s just made to look like one. It’s confusing to say the least.