I would think most of the story was in his imagination.
I do remember a time when i used to trail a deer through the forest that had plenty of wolves and be able to mooch into shooting range several times and not have to worry that that's the last chance i will get at making the perfect shot with whatever firearm i was carrying.
That is a thing of the past for the forest I used to hunt and that is totally due to the overrunning of said forest by the wolf that was hunted with the intent on killing every last one of them but was through that intent transformed into the most elusive predator the world has ever known. And that is my opinion.
The authors description of the need to finish the kill with his knife is a reality and I had to do that once and have always carried a hand gun when within the law to hopefully never have to do that again.
His description of the effect of the shot, the Minnie' ball, although possible, is I believe in this story a sensational exaggeration of a hyperactive imagination.
And I also hunt with a flint lock rifle, but I put my powder in the flash pan and my flint strikes the frizzen.