That's a great point - and this is an example of one of the poorly written questions on the LSAT. Capotorti's definition is standard in the international law field, but obviously you are not expected to know that on the LSAT. For this specific question, you are more likely to reach the right answer by process of elimination, though the statement that "considered a minority in all major European states" (lines 46-47) provides a hint that the definition applies to multiple states, i.e. international, rather than being specific to one country.