Answer:
Of course it makes a sound. This question is not supposed to be a brain teaser or and exam question, it is about nature and the connection between nature and humans.
It is implying that "no one" includes humans and humans only. A gopher or a bird might have heard the tree fall, but saying that "no one" was there is implying that no one human was there to hear it.
This statment is saying that humans always exclude nature itself from our language and that human and nature are two different things.
Hope that helps!