True - partly. Propane, butane and shellite are fossil fuels from oil or gas. 'Metho', which is really ethyl alcohol, is made industrially from plant material, often corn.
That said, I rather think that our use of propane/butane for bushwalking is unlikely to be significant compared to just about any other usage. In bad weather, not to mention in the snow, I find a canister stove very convenient compared to just about anything else.
But, HYOH.
Cheers
Roger