The plane was coming into United States airspace (and land) and therefor under the control of the United States of America, he qualifies for US Constitution treatment.

If he's on an American company's airliner, in Europe, we can deny them entry onto the plane - and we do. If it's a foreign plane, we usually set something up with that foriegn Government so we can do the same, but if not we'd let them board and then just not let the plane get to US Airspace (so, generally, those Governments hear that and just let us remove the person from the plane, otherwise no one goes.)