upwashing is somehow caused by the wing's approach.

On one level you can say it's a consequence of the bound vortex around
the wing. Not satisfying? I agree, but that's about as far as most
aerodynamics books go in providing an intuitive answer.

In another scenario, what happens in a long ducted fan? Is this
not analogous to a wing "pushing air down"?

You aren't the first to pose that question and it's a good one. Here
are some things which are unsupported by anything that I've read:
There is at least one dis-analogy (new word) that I can think of.
With a wing, it creates a low pressure area and then is gone; whatever
happens to that low pressure area is irrelevant. The air that rushes
into it has no effect on the wing. A fan, however, creates a
permanent low pressure area in front of the airplane, which creates a
flow from front to back which doesn't exist for a wing.