Upvote:4
Since the OP appreciated the reasons in the comments, and would like to mark an answer as accepted, I will summarize the comments.
It seems likely that since the flight was packed, the Emirates agent was likely looking for volunteers to get bumped off the flight and take a later flight. Various examples of reasons why more people were not asked:
Now my observations/opinion: If they did not need to bump several people, no need to announce over the PA that they need volunteers. And although the question almost sounded to me like, "Can you take a bus instead of a plane" it could have been what they are trained to say to be more formal way of asking "Do you want to take a later flight for a possible free travel voucher?"