New Zealand Fire Service specialist fire investigation officer Mike Cahill, of Invercargill, said the fire was started by some conductive material being blown on to power lines that night.
The fire, fanned by winds of up to 100kmh, razed the home of John and Pat Kerr and burned 40ha of land on the hill behind the town.
Several properties were evacuated, including the town's rest-home, and more than 60 firefighters and seven helicopters helped bring the fire under control.
Firefighters were called back to the area for several days to douse flare-ups and hot spots.
"We're not sure what the material was that was blown on to the lines, apart from it being some tinfoil kind of material," Mr Cahill said.
"It would have to be a reasonable size to stretch across the metre-wide gap between the high and low voltage lines.
"There's nothing left of the material.
It disintegrated when it was all burnt away."
Mr Cahill said the fire was no-one's fault, and there was no blame to be apportioned.
"With the information we have, there was nothing that could have been done differently, and those who fought the fire did as good a job as they could have."
Mr Cahill said he made no recommendations in his report on the fire that anything should have been done differently.
The cost of extinguishing the fire is not yet known.
