In our world, burning a log of wood in a campfire is a combustion reaction that uses the log as fuel. Burning a log of wood in a campfire in the other universe releases the “fire” element contained in the wood, as trees, and all living things in the magic universe, contain some degree of fire element.
What they call fire and what we call fire look the same, outwardly, but are subtly and profoundly different in their natures. Just as combustible chemicals do not react the same way when brought to their universe, the “fire” element doesn’t work the same way when brought to our universe.
This also why most forms of magic don’t work in our world. Ice Magic doesn’t work because there is no “cold” force. We have to rely on refrigeration technology, which creates a lower temperature (less heat) in an enclosed area by shuffling heat around. Fire Magic doesn’t work because there is no “fire” element in our world for them to draw from, and any fire element brought to our universe doesn’t work the same way when it’s here.
–Notes from a Senior Planeswalker’s Private Journal.