Not clear, whom told, or how did FD know about ammo?
Now a couple of us called the FD when a member passed away and the widow asked about some powder that had been in the attic for few years...we eased down slow upon seeing kegs of black powder, that's a bit different. Ammo and smokeless I subscribe to cool/dry/vented container.
Cooking off: well had the chance to test out some stuff when a farmer was building a pond, various ammo tossed in, yeah we took precautions. Loose ammo, boxes of ammo, no big deal, fireworks more dangerous. A box of sealed up tight 22lr in a metal box, made a dent. The worse offender, a disposable butane lighter. Reminded me of the time we thought if one stick of TNT good, two is gooder for a beaver dam...oops!