The US used the same weapons in Fallujah and likely elsewhere. They called it "shake and bake" when they first fired WP artillery to draw enemy fighters out, then followed up with conventional artillery to kill them.
Nobody can hold the US accountable, so they're not going to hold their rabid dog accountable either.
No, they absolutely used it as a ground-attack incendiary and have admitted as such. They were not flushed out by being illuminated, they were flushed out with choking smoke and burning shit raining down on their positions.
Even if they did only use illumination flares, there are considerations against using them in civilian areas in ways that can start fires or otherwise cause injury to civilians.
The legal issue is moot because the US was not an adherent to these laws until 2009.