Thanks for doing the research! I was also wondering if this statistic is somehow connected to the PPP valuation of China's GDP (as you know, China is now 'worth' 40% less, which can affect all kinds of statistics).

The briefing says:

The trade values used here are expressed in actual terms, not in terms of purchasing power parity (PPP). This is because the monetary value of internationally traded goods is recorded at international prices. So it makes sense to use a consistent monetary unit across countries.

The analysis finds out that in 2004, China `avoided' emitting around 381 million tonnes of CO2 due to the import of goods and services. At the same time, goods that were exported from China generated approximately 1490 million tonnes of CO2. The overall effect was that around 1109 million tonnes of CO2 were emitted by China as a result of net exports. This accounted for 23% of China's total CO2 emitted in that
year (4732 million tonnes).

I think that the changed GDP measure should not affect this, however I am not completely sure because the authors do not explicitly state whether they use the PPP measure for China's own GDP and I don't know how the % exports have of GDP plays into the analysis...

Whether Japan, South Korea and Singapore can be included in 'the west' is a flavour of the month kinda political question (the west being a political label for those who ride with US and are rich like US). I assume you'd have some interesting thoughts about the socio-cultural aspects.