Interesting.
I was reading a bit, and it seems that the standard theory is that the Polynesian migration began in Southern China, around the same time that these artifacts are dated to. So, we could very well be looking at the artwork of the people who would soon get pushed out of China by migrants from the north, and ended up colonizing all those pacific islands.
However, recent DNA analysis suggests the migrations may have started a couple millenia earlier, so who knows?