Narcissa knew that while some of what Severus would be the truth she also knew that he was being polite. He was clever enough to know that this wasn't just a social call- which was shown by what he said about being relieved of his responsibilities at Hogwarts.
"Indeed it is far to long between each visit," she said taking a seat. "Please join me," she said waving a hand at a chair. "Now that you do mention it I was wondering why you were let go off at Hogwarts," she said. Of course she had heard and read bits and pieces but she wanted to here it straight from him.