Can't talk to people in their language nor understand them -> fuck off the emergency exit
Sounds harsh but it is the truth.
Flight attendants are trained to scan passengers for potential trouble makers before the flight takes off. I am not saying that he did anything, but it might be that they felt that he is not the right person to sit on the exit row.
He also said that the check-in person cleared him to sit there. That person doesn’t decide it, it’s the personnel on board, who have the responsibility over the safety of the passengers and they have the last word.
Everyone who flies frequently, has seen similar incidents happen and it is not even that uncommon. Usually the people just change the seat and there is no further drama.
I have been on a flight from São Paulo to Amsterdam, where I saw from the beginning that there is one person who is going to be trouble. We ended up having an emergency landing in Lisbon, because that person decided to rip the toilet sink off and bite the flight attendant in the ankle, hit several other passengers and caused a total chaos on the flight.
After that I rather have all suspicious and un co-operative people removed from the flight, than take any risks. I don’t care how famous or rich they are, or what religion or race they represent. Khabib is being a Karen himself here and the fools attacking the airline complete idiots.