The only unexpected finding here is that this homo sp. got to an island that is surrounded by water. I have a feeling that this species is a Denosovian, but unless they can get some DNA out we won't know. We do know that the Denosovian knew how to travel over open ocean as they made it to Australia and PNG.
This is incorrect. We know Denisovans only from one cave in Siberia. From there we have DNA sequences, and from those we can tell Denisovans interbred with some homo sapiens, including people now in Australia and PNG (up to 6% of their DNA is Denisovan). There is no evidence that Denisovans themselves travelled that far.
There is one additional piece of evidence which is the modern Australian Aborignial and PNG population is descended from a founder population that appeared 15-30K years ago. Add all these up and the evidence is strongly in favour of the Denosovians being the first homo sp. that crossed the Wallace line.
Which is most likely what happened, IMO. Descendants of that population got outcompeted by later ooA migrations, other than small pockets such as Negritos, who also show high Neandertal DNA %.
https://academic.oup.com/gbe/article/9/8/2013/3952725
Malaysian and Andamanese Negritos don't.
This paper is very interesting though as it provides clues as to how the Denosovian spread through the Sahul. It adds even more support that the new homo sp. found in the OA are Denosovian.