This is another installment in Oda’s long-game Robin-defection drip: each arc beat (the Eternal Pose gift, the trap she doesn’t finish, saving Luffy, all according to plan, and now the civilian-save) is individually deniable but cumulatively load-bearing. The deliberate ambiguity (altruism vs. self-interest) is the technique — it keeps her allegiance an open question until the arc-end reveal.