Was Jared Diamond the only one to know this ?
He certainly mentions (a whole lot)New Guinea as a site of independent invention of agriculture in his book "Guns, germs and steel" .
An interesting point that he made is that being agriculturers allowed the New Guineans (highlanders in particular) to successfully resist the decimation that fell upon their indonesian and philippine cousins who were just tiny bands of hunter gatherers .

I'm pretty sure that rice was originally SE Asian rather than Thai. The Chinese originated in NW China, and China S. of the Yangtze was still not really Sinified at the end of the Han dynasty.