I think you are right, and the solution is a meta-textual reassurance, specifically of the form:
"if one of the statements is true, then which casket should the suitor choose?"
I agree, although note that Gardner actually sneaks in the subtly different statement "at most one of the statements is true." Of course, even here one has to be careful: do we require that the problem say "if at most one of the statements is true, and the previous description of the problem is correct, then …"? If not, what allows us to trust the previous description?
One can re-phrase every logic puzzle ever as "Assuming that `P` is true, what can you deduce about `Q`?"; or one may assume that a logic puzzle of the form "`P` is true. What can you deduce about `Q`?" is really shorthand for the former. I don't begrudge mjd for pointing out this shorthand, but I do think that his description of the 'solution' (to the meta-problem, not the actual puzzle he poses) is facile at best, and creates bigger problems at worst.
