So, the way the case is presented, it is first a market sizing and then a strategy case. But you can easily turn it into a market entry case if you want to. Many cases can be steered in different directions. As an interviewer, if you see that the candidate is comfortable doing the math, you might go off in a different direction, maybe ask some more challenging questions about market entry.
If you see that the candidate seems to be sloppy in writing assumptions down or mixing up numbers you might push harder on getting the math right.
The same goes for you as an interviewee: If you feel more comfortable doing the math, try to stay in that territory as long as you can. If you feel your strengths are more in having a wide-ranging conversation, try to go in that direction as soon as you can. If you're for some reason an expert on China, play that card. Always try to play to your strengths!
(By the way, steering a conversation is an important skill for consultants. So if you manage to set the pace and agenda in your interview, your interviewer will be impressed. Assuming he or she is not a self-absorbed jerk.)