In a book someone hears a woman voice and says:
心配そうな、お母さんの声
As far as I know, そう(な)
is to say something seems based on visual information, and my grammars agree with this: things like おいしそうなケーキ
. If linked to something you heard, そう
is used to report what you said/heard, like 明日だそうだった
, "I heard it's tomorrow".
Given the context, it seems to me that そう
is the first meaning, since the character isn't reporting something she heard.
Is that そう
the first meaning? If so, is that use wrong/unusual?