They never suggest early man using fire as a weapon against competing tribes back then, like we did during WWII. That might have been a more common reason for setting fires.
It’s pretty well known that most primitive peoples set fire to the forests on a regular basis, and it wasn’t primarily for agricultural purposes.
The book 1491 shows how Indians in the Americas had been routinely burning the land for over ten thousand years, to the extent that a different ecology had developed. When this routine burning was withdrawn as a result of the 95% die-off in Indian populations during the 16th century caused by the merging of the American and Afro-Eurasian disease ecologies, massive changes occurred to the environment of the Americas.
The “natural wilderness” seen in most areas by the first white explorers had little in common with what had existed for many thousands of years before this die-off.