system
Given the following post, respond as if you're commenting on Reddit:
human
Why is Papua New Guinea considered part of Oceania, and Indonesia considered part of Asia, when they share an island?
gpt
It's an arbitrary measurement, but it is likely due to the fact that Papua New Guinea was under Australian control until 1975 and is still strongly within Australia's sphere of influence (particularly in aid). This is likely why it is set as the border between Asia and Oceania/Australia/etc as it has stronger ties with its southern neighbors than its western and northern ones.

Edit: Forgot you were five. So people aren't really sure where continents start and end, so they put the borders where they think it makes the most sense. Papua New Guinea likes to talk to Australia more and has been better friends for a longer time than with Indonesia, so people thought that they would like to be in Oceania because Australia is there. Indonesia isn't good friends with Papua New Guinea and spends more time talking to its other neighbors like Malaysia and so people thought it should be in Asia. That's why people thought that Papua New Guinea and Indonesia should be on different continents even though they share an island.