I'm not sure that they can! Many will know the two flags go with the two countries, and here they can easily type in the second box if the first doesn't match. It may become moot, because by 2017 NZ will have completed its referendum on whether to change its flag.
It's 2020 right now. The referendum failed. In the end, the people got to vote whether to have this other flag or the one with the Union Jack, and the Union Jack flag won.
Silly me, here I was thinking that people would be able to identify very distinctive flags, such as Mexico, Cyprus, South Africa, but it appears people just start typing like crazy and start with the countries they know.
South Africa? It looks a bit like most African flags, but I get what you mean. The thing is, though, that on the quiz, they have a yellow box and you have to go in order. Although you are able to skip around, it is found easier by people to just go in order, skip the ones that they don't know, and go back to them later.
I got all of them apart from Netherlands because a lot of people get mixed up with the flags of Russia and Netherlands. People also can't distinguish between Holland and the Netherlands :/
Nice quiz, mate!