I, too, saw that on NBC and had a visceral, bad reaction to the way it was presented.
However, I want more info before I get angry. Clearly, the specific mechanism you outline from the NPS statement is dubious. That doesn't necessarily mean that the fire was NOT started by shooting.
The backstop (rubber granule stuff) at my local indoor range was caught afire not too long ago when some nimrod with a SCAR, trying to impress the girlfriend he had dragged to the range with him, let loose with an entire magazine of tracers as fast as he could pull the trigger. The fire was small and quickly dispatched. The smell of smoke didn't even make it from the range to the attached gun shop. The fire dept came out. The range closed for cleanup for a day or so. It can happen easily with the wrong type of ammo.
Also, given the volume of steel-jacketed and/or steel-core, copper-washed bullets used by American shooters every year, I'm not ready to discount the notion of sparks at impact. In 7.62x39 alone, surplus ammo and new Chinese ammo with *lots* of steel in the bullets was arriving in the U.S. by the container-shipload before the Clinton administration stopped it. I have a case of the stuff, myself, and the bullets are strongly attracted to a magnet. I've never sectioned one, but it's clear to me that they have a good deal more steel in the bullet than the "bi-metal" stuff commonly found today.
I'm accustomed to the media getting things wrong and it appears they probably got this story at least partially wrong from the beginning. That doesn't surprise me. However, if it turns out that there were some idiots shooting tracers into dry pine straw or high-steel-content bullets into the right kind of rocks, that wouldn't surprise me either. I'll keep watching both mainstream and gun-centric web sites for further info and withhold judgement until I know more.
If the National Park Service knows enough to make a definitive statement regarding how the fires started, then they know enough to file charges against the people who started them. We may not know the whole truth until it comes out in a legal venue...and maybe not even then.
For people who would like to do a little more reading, there's a decent local news article here:
http://www.heraldextra.com/news/loc...572a-a4c8-85989445763c.html?comment_form=true and a pretty good thread on thehighroad about the subject here:
http://www.thehighroad.org/showthread.php?t=664756