As far as I can tell, in this scenario, the journalist has powered off their phone, ignored the message about "findable when power off," and then is somehow tracked through the BT beacon and Find My network.

Were their phone to be on, all the same tracking would work.

Were they to read the message and go change the settings, this tracking would presumably not work.

That assumes you trust that the "always on processor" only does what it says it does, of course. But in that case, any proprietary device is just as bad as any other. (Many supposedly less-proprietary devices could be sneakily subverted, too, no?)