What was the "obvious" threat exactly INTRUDER? My interpretation is that something said innocently by a French national struggling with the English language was (wrongly) perceived to be a threat by an American crew.
For this, said person is now (rightly) released and yet (wrongly) refused entry into the USA. That tells you a lot about the hysteria and absurd logic which now prevails with the American authorities. The loonies are in charge of the asylum!
I work daily with a multitude of nationalities. Even though most have a reasonably good to fair command of the English language it is not unusual to find them sometimes lacking clarity when expressing themselves in non standard situations. American hysteria has programmed the public, airline crews, and officials to consider anything which they don't understand as a threat.