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.
That's the key point in my mind. It's one thing to show up at the airport and being told at the check-in desk that due to overbooking your seat has already been given to someone else. In this case he WAS ALREADY seated... meaning they had enough seats for everyone already seated.
They wanted to give preference to airline employees over a paying customer.
There are over a dozen daily non-stop flights from Chicago to Louisville, and untold more options for flights with one connection. Surely the employees could have still made it to Louisville without too much delay on some other flight... airlines always work with each other to accommodate situation like this.