That in the case of medecine B, there's a 66% that the result (600,000 people dying) is equivalent to the result of not taking any medicine.
Whereas when the problem is framed in term of gain, it's quite clear by the phrasing "66.6% chance that no one will be saved.".
That's the problem with this kind of questionnaire, and it's compounded by the fact that they do not provide the Korean/Japanese/French version of the questionnaire they used.