I couldn't find any information about how they were contaminated, whether they were grown contaminated that is, without being cut, or whether the people didn't wash the outside of the cantaloupe before cutting them open.
Unwashed cantaloupe causing sickness would make more sense. Theoretically the knife blade would cut through a contaminated rind carrying the bacteria to the edible inside.
A perfectly logical explanation. If that's the case, it must be a real virulent pathogen.