> now that I know
> the future, I would never act contrary to that
> future, including telling others what I know.
The difference between the universe of Story Of Your Life and a generic deterministic universe is that in Story Of Your Life free will is not an illusion; it exists, but it can only be experienced from a certain perspective, which is complementary to the timeless perspective.
Very possibly there is a third perspective in this universe which is also equally valid. We could have a sequel (Departure?) where we meet the aliens do exactly what I struggle to imagine: they can observe only the future, and their choices affect only the past.