At the beginning of Chapter 7, what does David find out about his mother?

From the text:

"The man had saved the woman's life because he liked her, in the way grown-up people like those they wanted to marry. He had not saved her husband because he hated him for being her husband. He had saved David's life because he was her child. He had not told her the child was still alive, however ... because the woman did not care for him, the man had got his revenge by turning David into a boy from a concentration camp."