This is an area that's quite familiar to me, as I've done a few circumnavigations of Kapiti, I've also landed on Fisherman's/motungarara before, as well as Brown's island next to it.
The tides through that area are vicious, to the point where a trip in the area has to be planned around them, you can't overcome the flow for any length of time, especially for a circumnavigation.
They were definitely lucky to make the island. I wonder where they landed? There are actually houses out there, on the northern end.