No, latency didn't come up. (I agree that could be a reason not to use a dynamic array.) They were hung up on the idea that a dynamic array must be O(n) because at least some of the appends copy.
You explicitly said they were hung up on the "worst case O(n)" situation, so I suspect they were concerned about the latency. Insertion into a dynamic array has a worst case of O(n) and an average case of O(1), no?
