You are probably correct
From the Organisation for the Prohibition of Chemical Weapons Web site:
These Military Chemicals are Not Considered to be Chemical Weapons
Incendiary agents such as napalm and phosphorus are not considered to be CW agents since they achieve their effect mainly through thermal energy. Certain types of smoke screen may be poisonous in extremely high concentrations but, nonetheless, smoke ammunition is not classed as a chemical weapon since the poisonous effect is not the reason for their use. Plants, microorganisms, algae, etc. which produce toxins are not classed as chemical weapons even if the produced toxins belong to that class. Pathogenic microorganisms, mainly viruses and bacteria, are classed as biological weapons.
Nevertheless, if napalm and white phosphorus were deliberately used against civilians, it could be a war crime, but not crime involving the use a WMDs.