Maybe so. But probably guessing targeting someone for a warrantless search would not be legal. That is to say, the cops can't follow a guy and wait until they're 100 miles from the border to pull them over and call over customs to search them. What may save Turnick is he was already being investigated and this search was clearly an endrun around needing a warrant.

It was an international return flight, 100% border jurisdiction.

I've heard that is a misunderstanding. It's 100 miles from a national border or at a point of entry, not 100 miles from any point of entry. It still covers like 50% of the population though.

My understanding is that it's "only" 100 miles from the coast/border, which turns out to be most major population centers.