Bernoulli's Principle states that "fast moving fluid creates low pressure". The guy created low pressure outside with the water and air moves from high pressure to low pressure so it quickly sucked out the air from the room which creates deficiency of oxygen in the room and fire went out. https://video.twimg.com/amplify_video/1802493842488209408/vid/avc1/720x898/oLLJ1OgP_YxTDJxq.mp4?tag=16