Well, yes, he only pretends to reason in logical absolutes...

... which was why I wrote "and propositionally" - because he does actually reason in propositional absolutes. I agree with your analysis but note that it is only a good strategy if it's true that one and only one cup contains poison (or the equivalent, that one and only one cup will kill the Man in Black).

On re-reading I may have lost that subtlety in the clumsy (parenthetical-filled) expression of the final line.