Of the interviews for Auster that I've read, I haven't come across this question. It's very specific, and unless you get the chance to ask Mr. Auster yourself, you're likely to never know for certain.
When I read this sentence myself, just 2 weeks ago, in fact, I didn't take it literally from the author's view. I only heard Anna's voice. (I enjoyed Schubert when I played piano, especially his energy. I don't remember much about Schumann.) I believe she was simply showing that she's educated and bright enough to have her own opinion.