If nobody cares it was overbooked or not - why is it mentioned repeatedly on this thread?
There are different rules for overbooking versus crew travel.
It was overbooked. It became overbooked when they took 4 seats away. There was fewer available seats than what was sold. It is immaterial that 4 of the seats were needed for their own employees. No one cares about the so call rules; rigged in the favor of the airline industry. . He was seated, and ready to fly, and they ripped him out of the chair to cover for their own incompetence.