The fantastical theories about iPhones communicating with each other about being kept without cellular access and rebooting based on what they were told by other phones do not check out. It doesn't make sense. Law enforcement has the capability to host properly signed cellular.
It wouldn't make sense for Apple to deploy such as strange and insecure take on it. They've deployed essentially the same feature we use in iOS 18.1, although we aren't sure when they enable it. We enable our auto-reboot feature by default with an 18h timer, which used to be 72h.