I remember similar stories in the press about fifty years ago, of ammo going off during a fire, and the firemen fleeing the scene.
Later tests showed that ammo still in it’s box will simply fly apart with a BANG but not hurt anyone as it is not contained.
I am reminded of a student on our school camping trip who threw some wood on a campfire. A few minutes later there was a big BANG and an empty .22 case hit him in the arm.
I also remember an eight year old ME throwing .22 ammo into a campfire just to hear it go BANG!
My Great Grandma swept a 22 cartridge when she was sweeping the house, into a fireplace, and it shot her eye out.