Quite strange. I had a delayed baggage a couple of times with EK and I never had to tell them what was inside ...
The baggage was not lost, and they just need to know what I bought for urgent replacement (for compensation and refund).
When the baggage is lost (never happened to me though), they need the inventory to assess the compensation amount, which is anyway limited by weight. But again, that's for lost baggage, not delayed baggage.
(I don't mind being corrected)