Tricky. Of course, when you think about being able to hear/produce the tones in Chinese, you do have to remember that all Chinese toddlers do this as a matter of course, so in that sense, an 8yo doing it isn't crazy in itself; what may be crazy is retaining the abilities that let you do that, even though your native language doesn't require it.
I don't quite understand what the piano teacher meant by her remark. For a start, presumably it's about what musicians call pitch, not what they call tone, since that's what's analogous to tones in Chinese. Does she mean that your DS is reading the music in the sense not only that he knows what key to press but also that he knows in advance what it will sound like? (E.g., if asked to sing the music instead of play it, can he do that?) Or is she talking about his ability to guess what logically must come next, if he's given the start of an unfamiliar tune? Both interesting abilities, but rather different.
