The question asks about parenteral administration of the vaccine (meaning, not using the oral route). Non-oral vaccines will not strongly elicit IgA response. Non-oral vaccines not super helpful in combating a gut mucosal infection such as V. cholera, where IgA is more salient. Not sure if this is the actual correct reasoning, but it led to the right answer.
Injection = ONLY IgG
Oral = IgG & IgA
Cholera is transmitted via GI (oral) route , so you'd need the IgA protection, since it's mostly IgA that protects from GIT pathogens