What can I learn about English pragmatics from this dialogue?

Question

Charles : How do you do, my name is Charles.

Guest : Don't be ridiculous, Charles died 20 years ago!

Charles : Must be a different Charles, I think.

Guest : Are you telling me I don't know my own brother?

Charles : No, no.

(Four weddings and a funeral, 1994)

I'm quoting the above dialogue from Pragmatics And The English Language, Jonathan Culpeper & Michael Haugh. The authors use the text to explain the concept of deixis, definiteness, and anaphora. Below is a part of the explanation about the dialogue.

The crux of the guest's confusion here is the guest has his brother in mind when Charles is referred to, and consequently thinks that Charles does as well.

Here are my questions:

1. How can it be that upon hearing the name Charles, the guest relates only to his brother who died 20 years ago? Is the guest really ignorant of the fact that there can be many people by the name of Charles apart from his brother who passed away 20 years ago?

2. Is there some sort of humour behind such assumption made by the guest?

I lack pragmatic competence in English language. Please help! Thank you in advance.

Answer 1

This was (and was intended to be) funny precisly because a sensible person would know that there are other people named "Charles", and particularly because the guest's brother is dead, the guest should know that the person introducing himself must be a different Charles.

This passage reminds me a bit of the much longer and much funnier sketch "Who's on First

Answer 2

This conversation is absurd on purpose. Four Weddings and a Funeral is intended to be a funny movie and this is a silly interaction that would probably never happen in real life. It's 100% a joke. Your book is overexplaining the joke.