Try to explain how the hidden content would be found? It effectively doesn’t exist until the password is in place. It isn’t hidden, it isn’t connected at all.

I’m no expert but I can imagine a scenario where an x-ray scan can notice an SD card embedded into the controller and flag that for follow-up

SD card the author says was added to offset the cost of eMMC but would presumably stand out as anomalous with whatever AI is classifying the scan