Why is the ending of "The Fish" is surprising?

A. The fish had smaller fish inside of it.

B. Other people have also seen the fish.

C. The fish escapes.

D. The speaker lets the fish go.

The correct answer is D because the last sentence of "The Fish" is "And I let the fish go." Telling is that the speaker let the Fish die which is pretty surprising taking into account what the speaker does during the story (poem).