Given the multi-million dollar settlement I am guessing things might not be as simple
Airport security might have followed orders but those orders couldn't have come by anyone but United.
The admission of wrongdoing came from the CEO:
>...Two days after the incident, Munoz issued an additional statement, apologizing and promising that such an incident would never again occur on a United aircraft. He said, "No one should ever be mistreated this way." In an ABC television interview, Munoz was asked, "Do you think [Dao] was at fault in any way?" Munoz responded, "No. He can't be. He was a paying passenger sitting on our seat in our aircraft."
https://en.wikipedia.org/wiki/United_Express_Flight_3411_inc...