Previously, I would always get this notification telling me to reboot because a system update had been downloaded. But a few days ago I was talking on a messaging app with the screen turned off. I noticed some debris on the screen, so I went to wipe it off with my sleeve. I was shocked when the phone just rebooted. Did I somehow manage to select "Reboot" from the power menu with my sleeve, starting from a locked screen?! That's what I thought until the phone rebooted and told me that an update had been downloaded and I needed to reboot (again).
This all matters because it wouldn't be so great if reboots were forced, either immediately or sometime after a system update. Apple does that, among others. It's a horrible policy that causes the baseband module to reboot along with the rest of the hardware, whereupon who knows whether or not it blurts out IMEI, which can sometimes occur even if one has no SIM.
If this is all due to my own incompetence, then I hope you've enjoyed the comedy relief. Otherwise please enlighten me.