Pyrolysing is different from combustion. In pyrolysis, oxygen levels are kept very low so the substance does not burn, it merely loses a lot of volatile content and rearranges.

Charcoal is the result of the pyrolysis of wood, and it is formed in small amounts when wood is burned in open air. Pyrolysing a lot would turn the entire thing into charcoal, which the author suggest could then be used in building materials to trap the carbon.