(Just standing up to be counted.)
"This is a puzzle, because on the face of it, the effect is the same."
If both (A OR B) imply C then A and B are both the same?
Or "actions are morally equivalent if (by some measure) they lead to the same result?"
A surgeon operates on Bob -> Bob dies. A thief stabs Bob with a knife -> Bob dies. The surgeon and the thief are morally equivalent?
The case of the Walrus and the Carpenter is only problematic if we assume that the Walrus is somehow obliged to actually help the Carpenter; but, with that assumption explicit, then Walrus is morally in error in both scenarios.
I think most people, at least in Western society, do not consider their help is owed. As humans, they will often cooperate but they get to choose with whom, when, and to what extent they will cooperate. Sometimes the cooperation is a "random act of kindness"; sometimes they expect reciprocation.
To intentionally do things with intent to harm another is usually discouraged unless in self-defense; to decline to help someone become better off -- is not only morally neutral, it's also necessary. (Consider that every moment that you are helping someone specifically, there exist billions of people whom you are declining to help.)
Everyone must make choices about how they will expend the effort of their day. Some of that effort must go to help themselves else they will not survive and their help will be available to none.
Seems to me that the choice not to provide information is not "less wrong," rather, it is not "wrong" at all.