[agret]

> This happens on a device with no apps installed, with no apps running. No Apple ID. Fresh install.

On a fresh install you have Software Update, News, Safari, iTunes Store, App Store, Stocks, etc. which are all going to be a part of polling for available push notifications. When a new device update releases you will get a notification about it, even without an Apple ID signed in.

Yes, locally running apps can trigger time-based notifications but all network-based notifications should be handled by Apple's push services as iOS doesn't allow long-term persistent background tasks due to battery drain and it doesn't make sense for every app to have its own individual polling occurring at random times.