The picture's pretty blurry and it's hard to be sure, but I think it's probably a Norway rat (the article doesn't say) - the tail looks quite short and the ear quite small, plus of course the large size. "[N]early 40cm" would indeed be extremely big for a ship rat, but is well within the range of a Norway - see https://www.stat.auckland.ac.nz/~smiller/rat_id
I suspect what's happened is that the people doing this trapping, being in a forest area, are used to seeing ship rats and haven't seen a big Norway rat before, and think it must be some kind of "monster". I've caught them this big in my backyard traps - I didn't measure the length of the one below, but relative to the size of the trap it looks pretty similar to the Rotorua rat. It weighed 417g. Apologies for all the blood!
Discuss natural history subjects not strictly related to birds. Reports of interesting mammal, reptile, and invertebrate sightings are welcome.
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I don't really think it's possible to say for sure what the species is given the quality of the images on offer - for one thing, the ears look to be intermediate between what I'd expect for ship and Norway rats. But at the least I don't think you can rule out Norway, and that would make the size a lot less surprising - if it is a ship rat, then it really is a whopper.