This story is a satire of Americans and of humans in particular through the way in which it shows how we can all have our credulity and gullibility stretched to breaking point when we hear a good story. In more specific, American terms, this tale develops cultural stereotypes of gullible more educated Americans coming from the east and going to the West where their notions of "civilisation" and learning are shown to be mocked and derided by the way in which they are taken in and deceived by more cynical and worldly wise individuals in the west. Note how this is signalled from the very first paragraph of the story:
In compliance with the request of a friend of mine, who wrote me from the East, I called on good-natured, garrulous old Simon Wheeler, and inquired after my friend's friend, Leonidas W. Smiley, as requested to do, and I hereunto append the result. I have a lurking suspicion that Leonidas W. Smiley is a myth; that my friend never knew such a personage; and that he only conjectured that, if I asked old Wheeler about him, it would remind him of his infamous Jim Smiley, and he would go to work and bore me nearly to death with some infernal reminiscence of him as long and tedious as it should be useless to me.
This opening paragraph sets the scene very well: the narrator has been sent by a friend to be tricked and to hear a story that will amuse him, as much as he describes it in negative terms. The tale that he hears is a classic American tall tale that becomes more and more ridiculous as the story progresses. It exposes in the reader, and in the narrator, a natural propensity to believe what we are told, and it is only after the tale reaches absolutely absurd lengths that we recognise how we have been seduced and tricked by the power of storytelling.