High-quality plastics are actually a better material than metals aand alloys for most structural purposes in cameras. They are better shock absorbers, transmitting less energy to the more fragile parts of the lens. Metal adds rigidity (so can carbon fibre), but a metal barrel doesn't do much for shock absorption.
Most likely, a Canon or Nikon lens would have suffered the same damage with a similar impact. In fact, many lenses (and other devices) are designed with a failure point, so that they break at an easily repaired/replaced poont, rather than in an expensive or hard-to-replace component.