I've always been under the impression that the CATI cannon was a full-sized tactical weapon, which I'd interpret to be at least, say, a three-pounder gun. In those days, that was about the bare minimum anyone, even poor rebels scraping for supplies, would think of using in combat. We're talking about at least a 2.9-inch bore.
The cannon pictured is in my opinion no more than a salute cannon, and no amount of legend and big signs will convince me otherwise. Salute cannons of this approximate size very often had no trunnions, and grossly oversized cascabels. They lacked trunnions for the simple reason that most of them were made from existing steel or iron cylinders, bored out, and trunnions would have to be added and were totally unnecessary for the purpose. I've never understood why so many salute guns had oversized cascabels, but they do.
In my experience in 35 years of cannon research and collecting, every time I hear a story about a cannon that was dug up somewhere near some old battlefield, it turned out to be total hogwash. The intent of the story is usually to reincarnate an ordinary salute cannon into a priceless historic artifact.