To visualize why there is yaw-roll coupling with dihedral, visualize a wing with extreme dihedral or better yet extreme polyhedral, where the wing has more angle at the tip than the root. Imagine a wing with so much polyhedral that the wing is U-shaped with the wing tips vertical. Now when the plane is yawed, it becomes obvious that one wing tip will have a positive angle of attack and the other will have a negative angle of attack. That also happens to wings that are angled less severely but to a lesser effect.