Whether or not it was the sole reason, the CBP document certainly made significant note of the "possible terroristic images" on his phone.

This seems to be a rather significant story for our age - border agents can search your private email and messaging history, then judge you based (at least partly) on content that you might not even know is there.

Do you know for certain that every image you've ever received in every messenger is "safe" in every context? I sure as hell wouldn't let anyone dig through my phone. They can steal ("confiscate") it first.

This issue is very much on-topic for HN.