It looks like Wilbur hit the water paths as drawn. It's hard to tell from the color information, though. The problem of flow channels is that even a 1-pixel error can throw the path of steepest descent to one side of the intended area. A flat area is ambiguous so the river may end up routed along the edge of a flat area because there is no water flow across that area.
Wilbur has a Fill Basins tool to enforce connected drainage. I don't think it will matter in this case because the drainage already appears fully connected (that is, rivers all flow to the edge or sea).