If I was a bad guy and had something on my phone I didn’t want border agents to see, I would wipe it.

And, not to be too cute, I would wipe it while at the other airport, before I entered American jurisdiction.

And say, come to think of it, how do you prove it was wiped while the agent was holding it? Maybe I wiped it a few hours ago, and it’s been in “airplane mode” ever since. If the government is going to make the assertion that it happened on American soil, don’t they have to prove that?

Whether they have to or not, they almost certainly can. Per the article:

Tunick’s Google Pixel was running GrapheneOS. This Android-based operating system is focused on maintaining user privacy with features like memory protection, auto reboot, and the duress code. The OS only supports Google Pixel phones from the Pixel 6 onward.

The duress code is an optional feature of GrapheneOS that allows a user to set a code that is different from the unlock code. If you’re worried about the contents of your phone falling into the wrong hands, you can enter that code on the lock screen instead of the unlock code. This immediately and irreversibly deletes all data and eSIMs stored on the device.

Tunick provided this code to an agent, who entered it on the phone, after which “the screen went blank, flashed several times and the phone appeared to restart.” All data on the phone was gone, but authorities confiscated it anyway.

With that evidence, it's going to be child's play for the government to prove he used the duress code. They'll be able to prove that what the agent saw is consistent with the duress code and not an ordinary unlock. They'll be able to pull the cell tower records in Atlanta to show that the phone had a valid eSim in place prior to the code being entered, which eSim was wiped from the phone.

Once the government established that the operating system had the wipe code on it, I think that they'd be able to persuade a jury that it's simply not a reasonable or credible explanation that he would have completely purged his phone in the DR rather than rely on the duress code. But if defense counsel tried to assert that the phone might have been purged in the DR rather than in the US, it's going to be pretty easy to prove that's false.