I believe this is the first time taking an RC section that I've seen a question ask for the 'main topic' of the passage. This question may have confounded me for that reason, as I have become accustomed to main point/primary purpose questions, that more so exemplify what the author is trying to establish in the passage rather than the particular topic that the majority of the passage is based around. I do think the 'main topic' of a passage and the 'main point' of a passage ought to be distinguished from one another, in most cases.
Often times, in the final paragraph of a passage, you'll see the author argue for his central point. After all the relevant exposition of the topic in the prior paragraphs, he finally makes an argument. In a science passage, perhaps he argues that there's a certain way that the studies he referenced should be interpreted, and that they're not presently being interpreted correctly by experts in the field (this is very general, I know). Anyway, this is precisely what's going on in this passage (though it's not a science passage). For the majority of the passage, the author discusses Korean Americans and the ways in which a union strike unified them and Korean natives around a common cause. Then in the final paragraph, he suddenly makes an argument, using the immediately preceding paragraph as part of his evidence (in other words, he offers his opinion). He argues that the union strike teaches us something important, and then espouses the lesson.
Now, I got this question right, but I literally circled three answers in the process, and then went 'I'll just go back to it after doing the rest of the questions for this passage'. It was tough to ascertain what exactly this question was looking for under the time constraints, given that I'm so accustomed to looking for the main point of the passage.
Anyway, I'm surprised that the test-makers didn't toss in the author's argument as one of the answer choices, as that would have been very tempting.
Do these 'main topic' questions still come up? I don't think that the main topic and the main point are always distinct from each other. In cases where the author introduces an argument early in the passage and then argues for it for the rest of the passage , then the main point and the main topic may be the same. But in most cases, I do think one has to make the distinction when given a question like this. For all you gurus out there, let me know if I'm on the right track with this, or if I'm off-base in even making a distinction. I should note that they actually do ask for the primary purpose of the passage in Q13, so that perhaps implies that the test-makers do generally make the distinction I'm making.