Here is a link to another forum post with significantly greater damage to the vehicle that I replied to.
https://www.autogeekonline.net/foru...paint-post1602755.html?highlight=#post1602755
I was a career firefighter for over 25 years and from the photos you included the fire department was using multiple hose lines with municipal water as the extinguishing agent. No chemicals were being added. The white spots were most likely by-products of incomplete combustion carried by the prevailing winds onto your vehicle. While the fire departments do carry firefighting foam, dry chemical, and CO2 extinguishers, and products for fighting Class D flammable metal fires, this was a typical structure fire. Once the electric and/or gas was controlled in the residence they are fighting a Class A fire, no special chemical extinguishing agents necessary. If your unable to remove these by claying or with a high or low pH product you may need to polish them off and re-coat the vehicle. That's what the OP in the link ended up doing.