Perhaps we'll never know what happened, but I know that the pilot would not have attempted to land near power lines except in dire emergency. They carry very detailed maps which have not only the location of standing hazards like trees and power cables, but they also phone landowners on the expected route (think how wide a territory that can be given the unpredictability of wind) to check for the location of livestock, crops and machinery. Little is left to chance. Perhaps a catastrophic failure of the gas bottle regulator, leading to uncontrolled burning?