That would be me.
Try to avoid projecting your own paranoias, prejudices and biases onto other people, it's uncool.
Please explain to me how, in the absence of sustained agriculture and livestock ranching, Australian Aborigines somehow getting to New Zealand will develop military power superior to OTL Maoris? Further, why they didn't develop it to an equal level here? Because talk of eating ferns isn't bridging that gap.
The prejudice is you believing aboriginal were not capable of complex socio-cultural institutions capable of forming mutual relationships with plants and animals in spite of the evidence.
Regardless the formation of agriculture in climates similar to New Zealand has occurred in Oceania, namely Highland Papua New Guinea.
The divergence of these proposed aboriginals is deep, the dynamics of these supposed castaways could be dramatically altered from their mother culture. However the knowledge is already there in aboriginal cultures.
Dry heaps of this grass, that had been pulled expressly for the
purpose of gathering the seed, lay along our path for many
miles. I counted nine miles along the [Narran] river, in which
we rode through this grass only... it was what supplied the bread
of the natives...
In 1870 Christopher Giles wrote
discovered a native granary. This was a rude platform built in a
tree, about 7 or 8 feet from the ground, on this were placed in a
heap a number of bags made of close netting. Dismounting, I
climbed the tree to examine the bags, and was astonished to
find that they contained different kinds of grain, stored up for
the winter, or rather the dry season
In 1823 Queensland by a castaway
in a short time we arrived at a number of huts, which had
been erected for the occasion. They were so numerous I
could hardly count them; and each tribe (for there were
many assembled to see the fight) appeared to have their huts distinct from the other .… The women of our party [eight or nine women, 12 men and 14 children] then immediately commenced building, and in less that two hours had finished five or six commodious huts, in which we all rested that night.
The formation of what we now see as hallmarks of Maori society only took shape the end of a rather loose and intense period of Moa hunting. With the collapse of the moa came the evolution of Pa fortifications in the Classical Maori Period that includes among other things storage pits for holding kumara and other roots.
But the thing is a prerequisite very narrow definition of Agriculture is not necessary to develop a form of long term storage.
Prestige foods can in and of themselves facilitate and dictate the direction of people-plant relationships.
A foundational connection to bracken starch can after the collapse of lowland moa and seal create a chain reaction of intense fortications, strong gift ceremonies were displays of wealth are shown to neighbors and even enemies in spiritual ordained times of peace. What was once "pounded wooden sticks sucked of starch" can turn into bowls of puddings, "cakes" and sweets that provides social clout.
The environment facilitates and bracken provides storage foods for fall and winter. As does the dwarf cabbage palm.
Mass gatherings, villages and rival groups etc... we see already in the PNW from Haida Gwaii down to Washington this, we know aboriginals did, we have a strong idea that prestige and social capital influencing energy expenditure to certain foods. This can manifest itself in a greater reliance to more consistent and higher yields that come with domesticated plants.
"if they didn't do that here why can they do that there".
It's a different place with different constraints and dynamics. Earlier humans are effected by the limits of their environments, their environments are not limited by them.