Considering that the word barbarian comes to us from Greeks describing any language that wasn't Greek as the like the baying of sheep I wouldn't take "bat-like squeaks" too literally.
Maybe he didn't embellish his stories, but he certainly wrote down a lot of things that were clearly folk tales and hearsay and of which he had no way to check the veracity. You can't really make anything of his reporting of "Aethiopian bat squeaks".
Oh and btw- he was not the only (ancient) Greek interested in a more rigorous look at history. You have probably heard of Thucidides, Xenofon etc.