Well, you didn't add the excerpt, but don't worry, your question can be answered without the text, as this is general knowledge and deduction. So, the main purpose of the jargon in any text, not just the excerpt you have, is to make the text seem more genuine and authentic.
The author wants the readers to be completely immersed in the story, to feel as if they were really there. So, jargon can help you travel to another place, at least in novels, where people speak in a different manner.
