This is like saying "wood burns, even when the tree is dead" but much, much slower.
The disequilibrium (sugars and free O₂) were produced by living organisms, and this is just the gradual drift back to a lower energy state. CO₂ is common in the universe, and not at all a sign of life. O₂ and sugars are rare.
This is honestly what I'm thinking. Carbohydrates and hydrocarbons will oxidize to CO2 and water in our atmosphere, and especially quickly at warm temperatures, in the presence of energy sources like sunlight, or in the presence of ozone or elevated oxygen levels. In general biological processes like aerobic decay are so much more effective that we ignore this, but it still happens.