I find it very hard to see why this might be the case given that all of the large Australian banks are already actively involved in the New Zealand market. Moreover, New Zealand already has an open and contestable banking sector. There are few regulatory obstacles to foreign banks entering New Zealand, provided that they meet certain minimum qualitative criteria.
One of the driving forces of such strong growth is that firms are expected to continue making fixed investment -- such as in next-generation cars and related to maglev trains -- from a long-term perspective. I feel that the mindset of firms in this region is always future-oriented, while also taking the present situation into account.