However, having read the passage that I think he is referring to, I think it more likely that John Tanner used gunpowder on the rotten wood in order for it to catch a spark. Here below is the quote in question:
"Owing to our hands being benumbed with the cold, it was long before we could extricate ourselves from our snow shoes, and we were no sooner out of the water than our moccasins and clothes were frozen so stiff that we could not travel. I began also to think that we must die. But I was not like my Indian brother, willing to sit down and wait patiently for death to come. I kept moving about to the best of my power, while he lay in a dry place by the side of the bank where the wind had blown away the snow. I at length found some very dry rotten wood which I used as a substitute for spunk, and was so happy as to raise a fire. We then applied ourselves to thaw and dry our moccasins, and when partly dry we put them on, and went to collect fuel [Page 24] for a larger fire than we had before been able to make".
Now although no mention is made here of using gunpowder, it is obvious to me that this method was known to John Tanner, and that he had used this method before. Note this earlier comment by John Tanner:
"Fortunately the water was not deep about the rock, nor between it and the land, and though a thin ice had formed, I was able to break it, and carry my children on shore. But here we had nearly perished from cold, as my spunk wood was wet, and I had no means of kindling a fire, until I thought to split open my powder horn, when I found in the middle of the mass of powder, a little which the water had not reached. This enabled me to kindle a fire, and was the means of saving all our lives".
Note also the term "spunk" is used and not "punk". This I think is the first time I have heard this term used for tinder rather than sulphur tipped splints which are known as spunks.
Here are a couple of videos I made on the use of gunpowder for making fire: