Spoken very softly and with his eyes focused on the carpet at his feet, she could tell that her son felt guilty about revealing the source of his knowledge. It shouldn't have been a surprise that he learned about her past from Ron's son, but it was. She would've assumed that Ron was as careful about keeping those incidents quiet as she. Too much reminiscing about the world before the Dark Lord came to power was considered disloyal. Once he revealed where he learned about the Philosopher's Stone, he kept going.