And why do you believe it to be so?
Correct, the Bible doesn’t claim to be given right from God, just inspired by Him. I explain why I think that’s a good thing here: What is meant by a "perfect" Bible? - #33 by thoughtful
If the Quran is not actually from God, then it still is wrong no matter what it contradicts.
Having a first one would be a crazy historical aberration. If the books, which were scrolls, had any meaning, they would have been used up and copied lots. What books do we have the first copy of?
Christianity doesn’t depend on total inerrancy. We don’t know there wasn’t corruption in the text for those fragments we don’t have but there’s good reason to think it wasn’t extensive since others were quoting it early as well. Can We Construct The Entire New Testament From the Writings of the Church Fathers? | Cold Case Christianity