[DHowett]

On Apple devices, I believe that remote wipe is "Change the encryption keys for the block storage. It's as good as random data now."

That might also be why a PIN is available for "stopping" the wipe. (As an aside: the group got what they wanted, and one of the members even seems remorseful: they have the PIN necessary to unlock the device, but this was never touched upon.)

At the very least, that is why iOS devices take split seconds to "wipe", as opposed to the time it would take to write thirty-two billion nul bytes to flash.