Possibly, the original Flight Attendant said something to the Captain. Pretty much everything that happens on or around an airliner is at the Captains discretion. The decisions can be questioned and challenged by the airline supervisors, the FAA etc. and the Captain can be relieved of duty by the airline, but its Captains prerogative to remove someone off their aircraft.
The other factor involved is CRM, Crew Resource Management. The days were the crew passively follow the Captains decisions are over, and for good reason. Captains are trained to listen to their First Officer and FA, and actively respond to questions.
This means its quite possible that the Captain didn't want his flight delayed, or cause unnecessarily tension on the flight with his FA, and so took the easy (but highly questionable) option to simply remove him from the flight.
Note: This should not be interpreted as taking the airlines side, just explaining my thoughts on the factors involved.
The other factor involved is CRM, Crew Resource Management. The days were the crew passively follow the Captains decisions are over, and for good reason. Captains are trained to listen to their First Officer and FA, and actively respond to questions.
This means its quite possible that the Captain didn't want his flight delayed, or cause unnecessarily tension on the flight with his FA, and so took the easy (but highly questionable) option to simply remove him from the flight.
Note: This should not be interpreted as taking the airlines side, just explaining my thoughts on the factors involved.