English Art/Literary Linguistics Southern dialect

I am having trouble understanding a phrase that I think may be dialectal (i.e. based on a grammar different from "American English"). It is spoken in the movie "Searching for the Wrong-Eyed Jesus". The context is a character telling a story about how his father's hands had been blown off by dynamite. The father was holding a stick of dynamite in one hand, a box of caps in the other, and smoking a Chesterfield cigarette (the narrator suggests that the ash on the Chesterfield gets really long before it drops) - the ash from the cigarette ignited the caps which ignited the stick. The phrase I'm not sure about is "he never did know what done it":

"And if there weren't fire in them ashes fell in them caps and set them off, he never did know what done it."

My intuition is telling me to expect this to mean "If there had been fire in those ashes, he would have died." But this does not seem to make sense in the context of the story (there was only one stick of dynamite and it did explode, and there must have been something in the ash to ignite the caps). So maybe "he never did know what had done it" means "that would not have happened to him"? (I do believe that "he never did know" is equivalent to "he would not have known").