I have to agree with haffiman37. It looks to me as if the strut broke, allowing the moving blade to come into contact with the hull (thus the "swipe" athwartships), causing the blade to break. Common sense dictates that a fairly significant impact would be required to do this. I have seen Autoprops throw a blade before, but never seen one simply break off. Unless there is noticable corrosion on the stub of the blade, it seems unlikely that this would occur. Even if there is corrosion, the fault is not in the manufacture of the prop. Further, although it is hard to tell from the pix, the broken end of the strut does appear to be corroded, which, if is the case, could certainly have caused it's failure.
In any event, I suspect you will have a difficult time getting Autoprop to accept responsibility. And of course Caliber was going to blame Autoprop for the problem. I think you were being naieve if you actually thought that Caliber was going admit that a broken strut was their fault.