It's possible that it was just a largemouth bass with a genetic mutation. These things happen all the time and it's what drives natural selection. Every species of animal on the planet contains within its DNA every gene it has ever had, but normally only our more recent, "successful", genes are expressed (i.e. the genes that code for a tail in humans are turned off during embryo development leaving us with nothing but a tailbone, and embryos have tails that are about 7 vertebrae long during development). What that means is that birds, which gradually evolved from dinosaurs over time, are still occasionally (very rarely) born with teeth or with less feathers and more scales, and can be genetically modified to be born with these characteristics also by manipulating which genes are expressed or muted.
So if a bass has some type of ancestor that had teeth and was more slender, it is possible that this mutation simply "regressed" to an earlier variation. Although mutation does not necessarily indicate regression. The sickle cell anemia gene after all was a response to help fight malaria in Africa. That is why African Americans have this problem. Their ancestors that had only the non-sickle cell gene died due to malaria. The ones who had only the sickle cell gene died because of sickle cell. But the people who had both genes survived malaria and survived sickle cell. That is natural selection. One condition is favored, the others die out, and the new one persists. So this could also just be nature "testing out" a new model.
If it was a hybrid of any type, it would either be sterile, or have reduced fertility just like wipers and saugeye. The only reason wipers and saugeye aren't totally sterile is because the two parent species are so similar. A bass and a trout would almost certainly give rise to a sterile offspring considering the species gap.
But in this case, I would say it's likely a simple case of confusing one fish species for another lol.
I guess it could also just be an extremely skinny bass. But that doesn't account for the more pronounced teeth.