Thats a pretty terrible question though since there are two equally valid ways of viewing the question the way it is worded. It's not talking aboit China, it's talking about people in China. People in South Korea eat more rice than people in Colombia despite both countries have similar populations. "Why does China consume more rice than America" is the actual question to ask yo try and get that answers.
The question isn't "why is MORE TOTAL rice eaten in China than America?"
There simply being more people in China doesn't mean Chinese people choose to individually eat more rice. There are other reasons for that per person choice.
Both are totally legitimate interpretations. It doesn't specify what they're talking about beyond "people in China" which can either mean individually or collectively. It's meant to be a trick question, though, which is why it's worded so ambiguously.