The right weather conditions included a lightning strike right on the pond which the coveted fluid was floating atop. Also, the mix of cold air and warm air would have to be present to cause it to go up into a funnel. The firenado sparked nearby trees on fire, by sucking up the fluid and then traveling toward the trees. It boggles the mind to imagine all the right conditions, including the whisky, which had to be present to cause this freak accident.
Source: Daily Mail