I suspect he set it on fire...................but will never know for sure.
All I know is when I got off the school bus that afternoon the barn was on fire and there was a lot of cars parked along the road. I was maybe 7 or 8 at the time............
Hay put away wet can certainly cause a barn fire.
**When I was a child, my grandfather’s barn burned down Lightning strike? Or hay brought in before totally dry? (Sorry for your Grandfather!)**
I was around 10 years old when a big barn, a little over a mile from our farm, burned down because of ‘tough’ hay. The farmhand said you could feel the heat rising up from the haystack when stacking those square bales. But the farmer that owned the place insisted it was dry enough to bale.
Several firetrucks showed up, but the roof was still intact. So the blaze was able to engulf the inside, despite the water being thrown at it at each end. The haystack smoldered for several days after the wood was all gone.