I don’t think it’s whataboutism. The OC said they do not understand how a human can fin a shark because it’s cruel. The GP comment provided an example (factory farming animals) that illustrates animal cruelty is commonplace. That is to say, if you understand animal cruelty in factory farming, you should be able to understand animal cruelty in shark finning. I don’t think the GP intended to dismiss concerns about shark finning because factory farming exists.