Some people learn set theory before data structures and algorithms. People focusing on math rather than computer science, for example. As long as we're speculating about hypothetical aliens, I wouldn't reject that possibility.
Arrays, linked lists, binary trees and mergesort could be more fundamental than the relational model, but the relational model in turn may be simpler than (say) red-black trees, BSPs, skiplists (depending on how the aliens view randomness), or OOP.
It's an interesting thought-experiment, though - if CS were being re-invented from the ground up, which things would be more fundamental and likely to be discovered first, especially with significantly different hardware?
