I opted against taking a burner phone—a move that some legal experts had advised, in the press—believing it would provoke suspicion, and simply decided to give my phone and social media a superficial clean.

But C.B.P. had prepared for me well before my arrival. They did not need to identify me at LAX as someone worthy of investigation: they had evidently decided that weeks before. […] In either case, a U.S. government officer must have read my work and decided that I was not fit to enter the country. Because Officer Martinez had apparently read all of my material so long ago, he didn’t even know that I had taken all this material down. What this means is that, by the time a foreigner cleans his social media in preparation for a trip to the U.S., as much of our news media has been urging us to do, it may already be too late.

This had nothing to do with recovering any data from the phone. The information was already known to them.