When there are software updates available, the following notification is displayed: System Notification Helper Software update notifications are available. I don't understand why the word "notifications" appears in that sentence. I'm being notified of software updates, so of course the notification is available. Perhaps it should be changed to "Software updates are available"? I wasn't sure which product to file this against, I'm using whatever update tool comes with Kubuntu.
This is part of the Kubuntu Notification Helper, and is not part of Muon. At any rate, this is a notification for software *upgrade* notifications, (notifications regarding recent upgrades) which are post-installation messages (e.g. firefox needs to be restarted) or prompts for the user to authorize a script that needs to be run.