Ya they just have to tell the pilot, then the pilot calls it in. Which means the pilot okay'd this too. And all they have to do is say someone is a potential disruption in the air or they can make up anything on you. Flight attendants actually have a lot of power in that way. But maybe they were shouting Trump 2020 on the plane and the flight attendant told them not to shout and they argued free speech and thats where it came from. Or maybe they were literally talking calmly and quietly amonst themselves and this still happened.