Money, even at state level, is not some infinite resource (and neither is time).
States put effort into what they consider worth investigating - no state strip searches every incoming traveller, and goes through every item in their possession - it's possible for them to do, and if they did they'd find a hang of a lot more contraband, but it's costly, time consuming, and politically risky.
If the idea is that there's no point in encrypting anything on a USB stick, and you just hope they don't look at it at all, sure.
But there is no threat model here that includes "check the USB stick" and does not automatically lead to finding and breaking "hidden" content.
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
But saying that, the sheer amount of fake flash storage out there now, that's just a glorified USB-SD reader in a box.