Sorry for the little toad's death . So we got 2 possibilities in here so far. Since this one "let you" handle it; did you washed hands and rinse them with dechlorinated water or wear gloves before handling toad? Reason is, our hands are exposed to many chemicals and produce skin oils that are harmful to toads and frogs.

Another possibility is that either had some pathogen when you got it, or got contaminated from the other toads with something they had resistance to; but he didn't. Will wait for questionnaire answers in case there are other husbandry issues.