He's out in-joke-ing me. West Island is a derogatory reference to Australia, implying it's just a minor territory of NZ (north and south island being 'mainland').
But, 'mainland' is often used by South Island NZers to suggest that the north island (by far the most populous) is nothing more than a secondary 'non-main' island.
yep. the 'mainland' in NZ refers to a chunk of the Sth Island - from back in the day when english migrants were busy recreating the english aristocracy.