Having ammo is a good thing but it depends on condition/state. I heard of this event back in 2009 at the Ventura Gun Show during setup or teardown, I forget the exact setting. During a previous show I bought reloaded 45ACP ammo from Edward Wyman because it was during the ammo shortage, normally would not buy reloads from an individual. His reloads were not really cheap but the ammo looked fine and he documented the load such as bullet, powder and charge amount.
The last time I saw him was at the Tuson show about a year later, I think. Edward is rather unique as a seller by being in a motorized chair. While the article below doesn't state the exact reason for his conviction I believe it was the lead he collected from ranges contaminating the ground. As to the cause of the fire my guess is corroded surplus ammo that became unstable in the summer heat of the garage.
I haven't seen nor heard of Edward since about 2010.
https://www.dailynews.com/2011/11/16...ard-ammo-dump/