[SamBam]

This passage is often cited by people (not you) who claim that before St Augustine's time people could not read silently. E.g. https://community.middlebury.edu/~harris/LatinBackground/Sil...: "There is no disputing the fact that the Romans read everything aloud, in fact they were apparently not able to read silently."

This seems greatly implausible. Consider, for example, the fact that the Roman walls were often covered in graffiti. The idea that a Roman would have to vocalize all of them to find one that seemed funny seems absurd. Further, there are examples in plays of a character reading a letter silently.

It does seem, though, that there have been times in specific cultures when reading prose or poetry aloud would have been considered the norm, and whether or not one could read silently, it wouldn't have been in anybody's habit to do so, because prose and poetry were "meant" to be read aloud. The notion, then, that someone could apparently "hear" all the musicality of the text while reading silently may indeed then have been cause for surprise.