This has nothing to do with the wood being too dry. It is very difficult to get wood to the point where it is too dry.
That walnut, and probably also the maple, shows severe grain run off. Not a little bit of grain variations, but like serious grain issues. The grain runs completely off the board in a one inch stretch of wood. Use both the maple and the walnut board only for (handle) overlays from now on and get a new board.
The second thing you should realize, is the place where it broke along the bow. It appears to be broken at the handle fade, or at least in some sort of transition. The handle looks like it popped off?? Hard to say from these fuzzy pics. Get your thickness taper to match the width taper: the handle FADES must not bend.