I get asked to unlock my dev laptop every single time I go from the US to Montreal. The TSA person sits there and waits for my WM to boot before waving me past.
It seems more like they're trying to determine that it is in fact a laptop and not something resembling one.
Might also be documenting serial number and identifying radios associated with your device. As a dragnet etc. Palantir and co love them some massive data hoards!
In EU normally BIOS startup screen is the point at which they wave it as ok.
Now I'm wondering what exactly they're looking for... What else could those devices have been?
That's been my experience as well. I've visited Sydney twice, and both times I've been asked to light up my devices. Granted, I was on work trips requiring three separate laptops which does probably look suspect, but once they were booted they did not request to browse anything and were satisfied to see them working.