(Disclaimer, I am a Christian but I am not a creationist) It was just as the Natives in America, Ancient Greeks, and just about every other pre-recorded civilization thought about the start of the world - someone made up a story that captured natural symbols in a poetic style, then it was passed along by oral tradition for many generations, becoming fine tuned so that all could remember the same story. Basically, the ancient Israelites did believe the Creation account to have theological/mythological truth, and it was societal decency to accept it as generally true, but to say that it was God who ordained exact details to a people who didn't even know how to write is a stretch (just as Nahum Sarna hypothesizes).
You may want to ask this question at /r/AcademicBiblical