From December 1938 to January 1939, peaked on Friday 13 January Black Friday. The fires burned 1.5 to 2 million hectares, including 800,000 hectares of protected forest, 600,000 hectares of reserved forest and 4,000 hectares of plantations. They killed 71 people and destroyed more than 650 buildings and the township of Narbethong. The fires affected almost every section of Victoria. Areas hardest hit included Noojee, Woods Point, Omeo, Warrandyte and Yarra Glen. Other areas affected included Warburton, Erica, Rubicon, Dromana, Mansfield, the Otway Ranges and the Grampian Ranges. The findings of the Royal Commission held after the fires were significant in increasing fire awareness and prevention throughout Australia.
Wikipedia has a list of fires, and it does not align with your chart.
https://en.wikipedia.org/wiki/Bushfires_in_Australia#Major_bushfires_in_Australia
It shows that the 1974/75 fires and the 2002 fires covered more acreage than the current fires.