There was an archery shop near Sacramento back in the 90s that had a wall of "Robin Hood" shots made on their range. They were mostly aluminum but some carbons. So the arrows were permanently stuck inside the other.
As I recall the legend, it was as Pat B described -- no other shot could have won except by splitting the arrow taking up the real estate on the target. Since even a minor deflection would have landed the shot less than perfect, splitting the arrow was about as perfect a shot as would have been possible.
I've often wondered what kind of point they were using? 2-blade head or bodkin? A bladed head could achieve that split a little easier, I'd think. But a bodkin or something like it would be quite a bit harder, if not impossible. But then I remember that it's just a story & I need to let it go.