What is the significance of the word choice in "The Ransom of Red Chief"?

The entire story is told by Sam, so the account is in the first-person and from Sam's point of view. O. Henry needed to establish that such a character was capable of writing what is actually a rather complicated tale. The author makes Sam seem like a con-man who is not educated and only superficially glib. The reader can sense that Sam has picked up a lot of big words in order to be able to impress the yokels to whom he and Bill sell bogus town lots and other spurious items such as worthless stock certificates and shares in abandoned gold mines. Sam is glib like a barker at a carnival. He may remind some readers of the two imposters in Mark Twain's The Adventures of Huckleberry Finn who pose as The King and The Duke and sometimes pretend to be Shakespearean actors. Like Sam and Bill, The King and The Duke learn that, as Abraham Lincoln may have said:

You can fool all the people some of the time and some of the people all the time, but you cannot fool all the people all the time.

The story is liberally sprinkled with Sam's pretentious vocabulary. For example:

It contained inhabitants of as undeleterious and self-satisfied a class of peasantry as ever clustered around a Maypole.

Philoprogenitiveness, says we, is strong in semi-rural communities;

There was a sylvan attitude of somnolent sleepiness pervading that section of the external outward surface of Alabama that lay exposed to my view.

Sam does not use big words solely to impress people. He is the type of person who loves to play with words. Under different circumstances he might have been a teacher, a journalist, or a lawyer. But he is obviously self-educated. He makes many grammatical mistakes. Although Sam and Bill are only a couple of cheap crooks who are guilty of kidnapping a child in an effort to raise money for a swindling scheme, we feel a little bit sorry for them at the end. Bill is not articulate, but he is good-hearted. Sam has never realized his potential because education was not as readily available in O. Henry's time as it is today. Both men have wasted lives. They are getting along in years but have only managed to accumulate $600 between them after years of running around the country trying to bilk the public. And they end up having to hand over $250 of their meager capital just to get rid of their "victim."

"Deleterious" means harmful. So "undeleterious," if there were such a word, would mean harmless. "Philoprogenitiveness" must mean loving one's children. "Somnolent sleepiness" and "external outward" are, of course, tautologies. O. Henry himself was guilty of using grandiose language for humorous purposes. Here is a sample from "The Cop and the Anthem":

The hibernatorial ambitions of Soapy were not of the highest. In them there were no considerations of Mediterranean cruises, of soporific Southern skies drifting in the Vesuvian Bay. Three months on the Island was what his soul craved. Three months of assured board and bed and congenial company, safe from Boreas and bluecoats, seemed to Soapy the essence of things desirable.