Yes, I think that you have properly diagnosed your broken starter. It looks a lot like it was broken by a violent kickback, which is exactly what you describe. I have only seen one other starter like this, and it was also on a 440. The damage was almost identical, and was likely from the same cause. Don't have kitties over it; it isn't worth getting worked up about. As you stated, this stuff normally doesn't happen to you, so it won't likely happen again.