New Zealand Weather Question

At several points in the series, they remark on how cold it is, and how Tui's chances of survival are impacted by the weather.

I looked up the weather for Glenorchy, New Zealand, which is supposedly near this town, and I found that the low temperature for the worst of July/winter there is 4 degrees (Centigrade. It's about 40 Fahrenheit).

I understand that different peoples' perspectives on cold vs. not cold are going to be based on their climates of origin, but...

HOW IS THAT EVEN REMOTELY COLD?!?! (Trust me, from my perspective, the caps are necessary here).

A silly topic, I know, especially for someone new to the board, but this is just so jarring to me that I had to ask for others' opinions, or see if someone can refute the weather site and tell me that it was actually something along the lines of -20C (-4F) or less in that part of New Zealand.