Your cuz is an idiot. When a hunter passes up a shot due to safety or chance of wounding the animal, he is demonstrating responsibility and respect...nothing less should be expected of any of us.
That said, depending on range a bullet can be easily deflected when the objectis impacted. There have been articles on this proving that the angle of deflection is worse when the object is closer to the gun than the critter. Think about it like this. You shoot at a feer and nick a limb close to you deflecting the bullet only a fraction of a degree but the deer is 75 yards away, you will most likely wound or miss. If the limb is only a few feet from the critter, you most likely would not notice a difference in the impact from point of aim.
I can tell you I have butched several deer with buck shot in them from idiots like your cuz who will shoot at anything they can see with no regard for if it can make a clean kill. I would say calling him an idiot is being kind.
Good for you. Have a great season.