They're now saying that the SWAT team used flashbang grenades that may have caught the cabin on fire and ignited Dorner's ammunition cache.
They might have, but problems with that theory are...
Flashbangs won't start fires. Designed not to. Tear gas or smoke can and sometimes will.
Burning ammo is a non-threat. It won't put you into emergency surgery, unless you get a piece of brass in your eye or something.