"Yes, but don't look at me, it's all him!" or "Yes, but don't ask me how he learned!" or just "Yes, he did" followed by "Search me" to practically any follow-up question. I think "Yes, he sure loves books" is also fine. Few people care, tbh - making clear that you aren't standing there wanting to be quizzed on it goes a long way, IME.

Email: my username, followed by 2, at google's mail