I think it's because he doesn't mean the country whose capital comes last in alphabetical order - it's restricted to the capitals that appear in the quiz that is mentioned. So Nauru-Yaren doesn't make it because Yerevan starts with Y but comes after Yaren, whereas Namibia-Windhoek does
This is a messy one… based on the fact that Estonia and Tallinn come after Ecuador, one would assume that this would be the answer? Since you’re asking for the country name, you’re bound to think the quiz is asking you to name the country beginning with each letter, whose capital would be listed last, so in that case, Tallinn would come after Quito, so Estonia would be correct? But instead, I’m supposed to see an E, list all the countries that begin with E, then work out Tallinn is last but that begins with a T, then figure out the last capital that begins with a T is Tunis, and as if by magic, the answer to the E question is Tunisia? Weird.