I heard that people nick named the barracuda's "cuda's" at the drag strip back in the day. Chrysler picked it up from there. It's just what i heard.
I read a story in a Mopar mag many moons ago how the term Cuda was started. It may not be true but it's what I read.
2 engineers from Chrysler took a 69 fastback 440 Barracuda out on Woodward on Friday nights to see how it stacked up against the other brand and makes. This was before 69' B, RB, block Barracuda's were being officially made. The crowds on the streets were the one's that gave it the nickname "Cuda." They heard about it and took the name back to the plant. The brand marketing team heard this and decided to use the name.