It is refusal --- The guest said an irrelevant answer. If he even said that he had a lot of work today, it would be also a polite example of saying excuse. It means that he refused the offer with clear words which explains he was not interested in the cup of coffee. In our culture there is a similar story. "A person goes to a neighbour's house and asked the neighbour to lend him a shovel. The neighbour replied his cow is sick. The man asked what it matters to the shovel? The neighbour replied 'if you understand I have already made you the excuse'.

Source author: Mohammad Daud Mahmoody dauodmahmoody@gmail.com