The Bavarian forestry ministry confirmed on Wednesday that Brunner tipped what he thought were extinguished ashes into a small forest near his house.
But a few hours later he found flames rising from the same spot and had to call the fire services.
"I totally underestimated it, it's really embarrassing," the minister told Bavarian Radio. "You can't be careful enough."
Half a dozen firefighters turned up to quell the blaze. The number was deemed necessary due to the heightened fire risk caused by a dry summer.
Brunner himself had repeatedly warned the public about the danger of forest fires during recent weeks.
The firefighters were able to dampen the flames before they caused any damage to property.