So this whole idea atheists and Bart Ehrman-ites throw around, that early Christians had no idea that the manuscripts we had were scripture.... but Peter is making exactly that case here!
People that hold that view (e.g., Bart Ehrman) assume a Hegelian view of history, thinking that orthodox christian doctrine didn’t develop until later. Although the evidence is that a high view of Scripture was paramount to both early Christians and in Second Temple Judaism.