According to how the news has been reported locally, the reason why they wanted to deplane the passenger was to accomodate four flight crew members from a partner airline (so not other paying passengers). Irrespective of the fine print, basically passengers already on the plane, possessing a regular, valid ticket, and not being unruly or disorderly, should - IMHO - only be made to leave if a voluntary agreement has been reached. Not forcefully. A major disaster in how the airline handled it in my opinion and the fact that they subsequently reached out to the passenger in question is a case of much too little too late.