I think objects with these shapes make similar sounds in the real world. Sharp shapes make percussive sounds. Round shapes make softer sounds.

Dog's have very good hearing, and their hearing must help them to model the world around them, to understand what different objects in the world are.

So I think it's less about linguistics and more about our audiovisual mapping of the physical world.

Then again, that must be where the origin of language evolved from in the first place.