Apparently the Pacific includes most of South East Asia.. or someone needs to go and look at a map...
Singapore has to be a decision for the author - it is "connected"(ish) to the part of Malaysia that is connected to Asia...
Pick the odd one out and it makes absolute sense as to why it should not be there.
Wikipedia. No mention of the Indian Ocean there. Although the South China Sea is considered to be part of the Western Pacific Ocean...
Good quiz though I managed to get them all.
You can see that northern East Timor touches the pacific.
I'd suggest you just choose your countries and leave it at that. Giving an instruction then including a country "because it is uncertain" means quizzers are even more in the dark.
edit: P.S. I enjoyed the quiz, always almost forget Vanuatu but that makes it easier to remember at the last second :)