law Enforcement Agencies have a history of using incendiary devices to end standoffs.
In 1974 the LAPD along with a number of other agencies used incendiary devices to burn the house suspected of containing members of the Symbionese Liberation Army (SLA). 5 dead 3 from gun fire and 2 burned.
In 1985 Baltimore Police dropped an explosive device on an explosive device from a helicopter on a row house occupied by members of MOVE. The device ignited a fire and destroyed several adjacent homes. Police fired over 10.000 rounds. The single survivor and decendants were awarded 1.5 million.
1993 Waco TX the BATF botched a raid/publicity stunt on the Branch Davidians. They used burning munitions/incendiary devices in their final assault. The Treasury report revealed that the fire was intentionally set by the Government.
These are three high profile events were the police knowingly used a device to burn out suspects.
My point is that Law Enforcement knows full well that a burning munition is also an incendiary device. They know that when such a device is used a major fire will result. In this case they were lucky that the forest was wet and they did not create a massive forest fire and burn down a bunch of expensive cabins owned by rich and influential people.