That wood is left on the ground to regenerate the forest. Is a common practice. Without that the ground will not be able to feed again the existing trees. Also inside the dead trunks it creates mini habitats for all kind of insects, small animals that also feed the forest.

If you ever see a "clean" forest without dead trunks , leaves, kindles than that forest is a dying forest.

Read more about regenerative forest.

The fire was manually /intentionally started, not because of some dead trunks in the forest.