WP is used in artillery and mortar shells, which are predominately indirect fire weapons - meaning the person firing doesn't see the target, but must rely on an observer. This might've led to the reports of troops indiscriminately firing and not knowing what they're shooting. WP is the only smoke US mortars commonly carry with them. It builds up faster than HC smoke but doesn't last as long. HC smoke is not always carried by US artillery and is often supplemented with WP to build up faster.
We call firebombs "NaPalm" b/c that's what our first firebombs were made of. We also refer to the graphite of pencils as "pencil lead" and fuel for the HMMWVs as "gas" even though it is diesel. Jet fuel is kerosene, which is much different than gasoline as used in previous firebombs. Kerosene is a convenient incendiary b/c the aircraft use it themselves and stock it; it readily covers an area and is more stable than gasoline.