It is not preferential. At the and of the day just one member is elected, sometimes with only 50.1% approval from the voters. The preferences of the other 49.9% are ignored. The Senate is preferential because a cohort of voters is electing multiple members. The votes are tallied and handed out by preferences. Say there are five seats. Labor gets 60% and Liberals get 40%, so it’s 3 seats for Labor and 2 for the Liberals. Everyone’s preferences were considered.

The non-electorate seats in NZ work the same way, using a national tally to hand out those seats by preference.

Instant-runoff is just a way of having a bunch of first past the post elections in one go. “If this candidate was eliminated, who would you vote for? Okay, but if that candidate was eliminated, who would you vote for?”. That’s how non-instant runoff elections work too. Until eventually you’re left with two people standing and one has more overall support.

Edit: As well if someone gets more than 50% first preferences they just win outright. Just because we use the word preference to describe that doesn’t make it preferential voting. It needs to represent the vote of all people.