Agreed. Slavery, tariffs, and other reasons all fall under the same economic umbrella. There wasn't a slavery answer option. While slavery is a human rights issue, it was more of an economic issue to the southerners.
But that requires you to adopt the the perspective of the southerners to answer the question "correctly" under the test. Just because they defined slavery as an "economic issue" rather than a "human rights" issue doesn't mean that a) the war was not fought over slavery and b) that slavery is not a human rights issue.