Coexisting for thousands of years, then suddenly wiping out 32 genera all in the same century beggars belief.
As I'm a New Zealander, I'm far more familiar with mass extinctions in NZ, and let me just say, to paraphrase a Smash Mouth song, well, after the arrival of humans, the extinctions start coming and they don't stop coming.
For a few reasons.
1) Introduction of the kiore (Polynesian rat) - while now, somewhat ironically, nearly extinct in NZ due to competition by Norwegian and black rats, its predation of chicks and eggs was instrumental in pushing some endemic species to extinction.
2) Unsustainable hunting, and collection of eggs. The most prominent example is the thousands of moa and their eggs found in the middens of what was probably the first archaic Māori (aka "moa hunter") settlement on Te Waipounamu/South Island. Given that moa, like other large birds, were slow breeders, it was inevitable that moa populations would collapse shortly after human arrival given the level of exploitation seen in the middens.[1]
3) Fire. Archaic Māori used fire to drive forest dwelling moa for hunting, which destroyed large areas of old forest that were stable, but unable to re-establish under changed climatic conditions. For an example, the Mackenzie Basin[2], and the Torlesse Range[3], both now known for their extensive tussocklands, were previously covered in dense forest, which no longer existed by the time of European colonisation. With a loss of habitat comes increased risk of extinction.
4) Desperation - as moa became scarcer, the archaic Māori switched to alternative food species, and extinctions rapidly followed (e.g., the flightless South Island goose[4]). This is also the period where (most archaeologists agree) the ancestors of the Moriori[5] departed from the South Island and settled the Chatham Islands/Rēkohu, as archaic Māori society entered collapse.
I highly recommend this book[6] for insights into at least one confirmed example of the black hole theory. You can also explore the art of that book in the national museum's collections[7]. The fact that there's six pages of that art is rather depressing.
[1]: https://www.researchgate.net/publication/258344644_History_o...
[2]: https://en.wikipedia.org/wiki/Mackenzie_Basin#Environmental_...
[3]: https://www.arthurspass.com/index.php?page=225
[4]: https://nzbirdsonline.org.nz/species/south-island-goose
[5]: https://en.wikipedia.org/wiki/Moriori
[6]: https://www.tepapa.govt.nz/about/te-papa-press/te-papa-press...
