The only non combustible wall that would be completely non combustible would be a cinder block building that has no wood or other combustibles such as wood, drywall etc.
Even if you do have bricks up behind your wood stove on the wall the wall can still catch fire if the heat that gets too the wood behind the wall is hot enough.
That's why you still need to keep a clearance of 36 inches between the hearth, wall, and the stove as well as the stovepipe as although bricks aren't combustible they still are not a heat shield to the wall behind the wood stove.