It has no connection whatsoever with the "South".
In general, I think asking for clarification is better than being condescending.
I spent a fair amount of time researching this urban legend earlier today. I wasn't "assuming" anything.
But to make clear what I was saying, I really should have responded to the parent, who says: "It's extremely hard to believe that even a malicious scientist could convince himself that a horse cannot be ridden into town."
My point being that a malicious test-giver could certainly deny that as a valid answer. I don't know that I believe that anecdote happened, but it is assuming good faith to think that it couldn't happen because no one would ever reject "horse" as an answer.
Until someone provides an actual citation to a first-hand witness, I'm going to go ahead and call this myth busted.
Don't assume good faith.