Yeah, it's cast for sure...you can tell by the thin parting line in the first picture. I've seen failures like this caused by beating the timing gear and/or the harmonic dampner onto the crank instead of pressing it on using the correct tool. It doesn't break the crank when you do it, it just starts the tiny stress cracks and the normal twisting of the crank as the cylinders fire when the engine is running does the rest.
