The words, ‘this was the scroll,’ imply that previous verses (in chapters 2 to 4) were pre-recorded history. The dialect dates it to around the time of Moses.
From the references to the Assyrians and Ethiopians (Kushites), we see that was written sometime after the Downpour. Therefore, it appears as though this chapter had been rewritten into the dialect of Moses from some much older documents, perhaps even from the time of Noah’s son Shem.