Your interviewer will likely ask a range of experience- and knowledge-based questions. You might find hints regarding what topics they'll cover when you scour the job description, so be sure to have it on hand during your preparation. In this case, the interviewer is referencing your experience with large data sets, which are quite common. So, even if you might not have considerable knowledge or experience with data sets in the context of this particular position, you should be able to demonstrate how to handle data and how to incorporate it into your writing.