Article 11 of the Ryanairs Terms/Conditions clearly states.
He should have been removed. IMHO
Article 11 - Conduct aboard aircraft
11.1 General
If, in our reasonable opinion, you conduct yourself aboard the aircraft so as to endanger the aircraft or any person or property on board, or obstruct the crew in the performance of their duties, or fail to comply with any instructions of the crew including but not limited to those with respect to smoking, alcohol or drug consumption, or behave in a manner which we reasonably believe may cause or does cause discomfort, inconvenience, damage or injury to other passengers or the crew, we may take such measures as we deem reasonably necessary to prevent continuation of such conduct, including restraint. You may be disembarked and refused onward carriage at any point, and may be prosecuted for offences committed on board the aircraft.