Would it have been wiser if that person had, as a US citizen, just refused to provide a PIN? At the most they'd just confiscate the phone, and it'd be encrypted anyway. No actual destruction of anything.

On another note, maybe GrapheneOS should add some kind of feature where the phone involuntarily destructs if a correct PIN isn't entered for 48 hours (or whatever the user sets at installation time, and changing the value should not be permitted). That way the trigger for the wipe is the confiscation, not the act of entry of a duress PIN. You could disclose the mechanism to the officials who intend to confiscate, and also say (truthfully) that you have no control over the feature.