To get the right answer to that question we would have to go back in time and talk with Ho'ace, a paddler at the old Beaver Dam Lake Club at Tunica, MI. He coined the name based on his interpretation of what the big gun sounded like, with the WW Super-X shells that Nash used in it, from across Beaver Dam Lake. Many of us that hunt the lakes and swamps have heard the hollow sounding report of a big gun in the distance, as the sound filters through the cypresses and buckbrush across water. Nash wrote what Ho'ace said it sounded like as best he could, which ended up Bo Whoop.
Interesting side note on this, the gentleman who restocked the gun, and broke the news to the owner what he actually had, told me that he and another fellow or two took the gun down in the swamp near where he lives and one fellow fired it while he and another listened from a distance, to see if possibly made any unusual sound that would have led to the story. It didn't, but he was quick to point out that the exact location would have had to be used. I would add, the same climatic conditions as well.
Ho'ace was quite a character and storyteller who evidently was very gregarious, and he well knew that his employers and friends very much enjoyed hearing his tales. I know, and have known, several in my life like Ho'ace, and my life is much richer for it.