So... There's this thing in call phones (all of 'em): The carrier section that owns the sim (or soft-sim nowadays) and controls connection to wireless infrastructure. This is an enclave of chips and code over which the carrier has total jurisdiction. It's goings-on are totally separate from the normal OS and UI in the rest of the device. There's no conventional way for ordinary users to control, view or audit what happens there, because the rest of the phone isn't even aware of it; the rest of the phone knows only that there's active transceiver interface (its dial-tone, if you will.)
So... A phone appears to power off. What powers it back on? OK, we know there's no such thing as power-really-off-off, just states of standby. So, what is running in there that drops service to an off-like state, but has enough control to resume or reboot? And what might such a process be doing while its playing opossum?
Ya know who DOES have authority to control, view or audit what happens in the carrier section (besides the carrier, of course)? People with Stingrays or Crossbows.
Ya know who DOES have authority to start an iPhone from what is ostensibly its deepest state of standby? Apple inventory clerks, using their new Patch-O-Matic to update iOS on phones still shrinkwrapped in their boxes.
It's not a huge reach that a mix of carrier and vendor software could have been glitching restarts and standbys over the years as updates roll out, some perhaps specifically for such contingencies. And of course, there's no telling how much black-on-black subterfuge phone vendors have to play along with, in the interests of national security - which is increasingly at risk.
Or maybe it's just dumb battery software losing its **** because of the latest calendar calculation bug. I don't get worked up, way or another. I like toys. Apple makes pretty good toys. Every toy is flawed. How it is.