I'll take stuff that never happened for $1000
Theres no doubt this story is mostly made up. Small arms ammunition, as in 12.7x99 and down, is not dangerous in firefighting operations outside of being fired out of a firearm. Otherwise it's simply a small firecracker and bunker gear will stop the trivial fragmentation.
Perhaps a few of the powder cans made some good poofs and small booms, but thats about it.
As far as firefighting, they in the photo arent even trying to put it out, and they really dont need to bother. The roof is gone, perfect, let it burn itself down and then deal with it. Looks like the firefighter is standing on an uncharged 2.5 inch smoothbore, so they are just hanging out watching it burn. That line could reach into that bay and start to beat on it. The lame 1 3/4 foam lines it looks like they tried wouldnt be so great unless they were using them in the same exact spots.
This is a perfect scenario for a firefighter. Its stuck in a box, the box is already mostly open and you can see the entire space. Nothing to get hose tangled on, walk up and shoot water at it. 10/10 easy and fun fire to deal with.
BUT FLYING BULLETSSS121111111111111111111111111