You might want to reinforce that section of your bow. I was thinking the same thing that the arrow had nothing to do with the cracks, as I don't see how it would be able to crack the wood, and not have any damage to the arrow. But like I said it could be grain run off, or like DC said, cracks radiating out from the knot. But a little reinforcing patch on the back, and around the knot, or even some super glue. Or Gasp..... Fg cloth, and epoxy, sanded smooth, and it will be clear, and look normal. But it would be a good safety in case it suddenly decides to go to the dark side of the force......If you want to stay strictly primitive, you could use a very thin piece of raw hide, and hide glue, but it would be a good safety precaution, either way. You can fill in the knot with epoxy, or super glue. There are a lot of ways to repair, or stop a failure from happening. Some one with a whole lot more knowledge about such things,than I have, on here can help you with that. It is just what I would do. But I am not a bowyer, so it would just my guess as to how to go about it.
Wayne