RE: What the heck happened? I am really confused!
I am not going to comment on your shot selection. Live and learn on that one.
I posted about a doe I shot recently and ended up being lucky.
My deer was quartering away and the shot went a little high. It looked to be dead on. I was hunting from the ground and ended up shooting her in the neck. I found the arrow but it did have blood on it. She ran like the dickens and I didn't find blood for about 70 yards I think and then just a drop. I kept trailing her and finally found more about 20-30 yards further. I could hear her gurgling and coughing further in and waited for awhile. I ended up finding her another 30 yards away.
My point is ....... you very well may have neck shot it but the absence of blood or anything puzzles me. May have deflected off the neck and just karate chopped it in the throat causing it to try and catch his breath. Who knows.
Good luck in the future.