The single line part also requires you first set up an app to execute that code as well.

I think you skimmed too fast. Widgets, allegedly, are eagerly evaluated when an app is opened, and the system keeps trying failed attempts:

> After restarting, as soon as SpringBoard was initialized, the extension would be woken up by the system, since it had failed to produce any widget entries before, which would then start the process all over again.

The article claims that they had to manually cause the widget to crash so that the result doesn't get cached, right? So that's at least one line to trigger the reboot, one line (likely more) to register as a widget, and one to crash it.