Intriguing. Although don't trust one offs counter trend, could be anything from data collection, to a one off skewing the comparative month on the other end. Also completely rubbish weather in April. Lets see what June brings. Next month there are changes to Working for Families - likely to stimulate further credit growth.
I use the Household Balance sheet, Consumer Loans. https://www.rbnz.govt.nz/statistics/c22. Which released data shows continued steady credit growth from early 2014 through to current. Mar18 (16.4b) being 7% above Mar17 (15.3b).
Another good proxy is new motor vehicle sales https://www.mia.org.nz/Sales-Data/Vehicle-Sales. Which is still cracking on superbly. I just do not believe their is anything fundamentally different in credit, all seems to be typical mid/late cycle behaviour.