To be an island country, the country need to be located enterly on islands. The most of Australia is located on the mainland, so of course, it's not an island country.
I think, to clear this up, an island and a continent are two separate landmasses based on size. Australia is probably too large in size to be considered an island. This is why it is instead considered a continent. Good quiz, tho. It deserves all the takes!
Good idea for a quiz! If you need guidance, you are welcome to use my "All Island Countries of the World Quiz".
im not including australia i will add a caveat
Also, I don't think you added a caveat...