To interject, to me it seems that it is actually a counter-example, and I do not follow your reasoning. (A)'s argument is that murderers are criminals, but thi

To interject, to me it seems that it is actually a counter-example, and I do not follow your reasoning. (A)'s argument is that murderers are criminals, but thieves are not murderers, and therefore cannot be criminals. The lack of logical validity of that argument aside, (B) refutes it instead by providing (quite literally) a counter-example: (A) is both a thief and a criminal. Therefore, if (B)'s assertion is true, (A)'s argument cannot be correct, for if it were correct, then (A) could be a thief or a criminal, but never both. Since this is a logical argument, it prejudges the matter to conclude that the standard of evidence required for (B)'s assertion should be any different than that for (A)'s assertion. We know (A)'s assertion to be false without any extra information. If there were external details of evidence that could be introduced, then (A)'s assertion would still be false. (B)'s assertion, however, might then still be either true or false, depending on the extra lemmas. As the example does not make additional information necessary and does not mention additional information, it is an error to arrive at an interpretation in which additional information is required to make sense of the matter. (One can always arbitrarily arrive at such an interpretation.)