David,
I think your explanation is very possible. I'm a honed edge guy because I believe that this type of edge produces increased blood flow and reduced clotting but even I was amazed by this particular case. So I sent the pics and story to a DR. friend of mine and this is what he said about it:
The extensive external bleeding is no mystery at all. Obviously there was no lung collapse, so relatively little thoracic space was available for internal pooling. The aortic artery carries a huge volume of blood (it splits at the hips, forming the 2 femoral arteries, and you know how fast a deer bleeds out if just one femoral artery is severed). Even when merely nicked the volume of blood loss from the aortic artery would be large and, with the lungs not collapsed, much of the blood flow would be forced out through the only outlet available; the entrance wound.
Now, that would certainly account for the massive external bleeding... As for the lack of penetration, I guess we'll never know for sure what caused that. Thanks for the input,
Ron