Maybe he means that each interview of a citizen is causally independent, since interviewing one of them won’t causally affect the answer of another.
You could analyze the interview as adding a perturbation to people’s “pre” responses, and per jsalvatier’s comment, say that those perturbations are conditionally independent, as conditioned by the pre responses.
But it’s the independence of the response that matters, and it’s not independent of the stories and folklore.
Maybe my confusion can be clarified by showing a case where you have logical dependence but causal independence. I’m not seeing it. Jaynes uses inferential reasoning using backward in time urn draws as his go to example for causal independence but logical dependence. But that still seems a case where there is shared causal dependence on the number and kinds of balls in the urn originally.