CS is an intersection of arts, science, engineering and maths. The algorithms and data structures are the maths and science side, HCI is the arts/social science

CS is an intersection of arts, science, engineering and maths. The algorithms and data structures are the maths and science side, HCI is the arts/social sciences portion and of course applications, teams management etc are more where it intersects with engineering. HCI is a less grounded than the maths portions which are as much a science as any part of maths is. But still have a grounding. The engineering side is probably a lot more wishy-washy and concerned with anecdotes than empirical evidence. That's my opinion as a generalisation.