Deer have reaction capabilities that we mere humans cannot even begin to comphrehend. They have to...their lives depend on it.
Now in your friend's case, I will mention a couple of points, that MAY apply, as I was not there and didn't see it.
1. The deer may have not known that he was there (if it had, he may well have never even gotten the shot off in the first place), but the deer could have been in "alert" mode due to a trace of scent (from either your friend, another deer, coyote, 'coon, etc.), or maybe your friend had used a call of some sort a while before it came by. The deer could have just simply had a case of the "willies", as they are wont to do. It doesn't really matter what caused it.....if it was in even a reduced alert mode it's reaction time is even that much more quicker.
2. If the deer was standing still when he shot, and not engaged in an activity like eating, or sniffing another deer, then it could very well "jump" even a fast bow like as Mathews. They ARE fast, but the last I looked, they are stil NOT supersonic.
This is the reason why I like to shoot at a deer with an arrow as it's taking a step forward...preferably the inner front leg coming forward. A deer that is in motion, sacrifices a bit of it's ability to react. It may not be much, but that nano-second can be the difference between a hit, or a miss/wound.
As I learned to bowhunt after several years of gun hunting, I realized that one of the more difficult aspects of making a good killing shot on deer with the bow, was learning WHEN to shoot. This is one of those things where experience is not only the best teacher, but maybe the ONLY one.
This is also why I like to shoot at deer that are engaged in feeding activity, as they are mentally occupied with food, and their head/eyes, while always in defensive mode, are more occupied with where the food is, and that will gain you some precious seconds.
Offer No Apologies.....
NRA Endowment Life Member