It says all the children were given an option to pick up to 3 answers.

Mmhmm, I also noticed that, which is why it's the second sentence in my post.

Given the small sample size

It's a survey of 3,000? It's still possible that only one person was giving the survey to the Chinese students.

But yeah, it does look like the Chinese students got different instructions or had them explained differently or something. Just a strange poll.