I'm pretty sure this is exactly what was his inspiration. Real life assassins (ismailite dudes from Alamut, Syria) have mostly been famous for inventing suicidal terrorism, using hashish to brainwash their fanatics and have been stomped by Mongols long before masons even entered the picture. Obviously in reality there is exactly as much common between assassins and masons as you would expect from completely different organizations existing in different geographic locations and times: basically nothing.