No, I know he didn’t, but other members asked where they should aim off to compensate for the angle. General rule is steeply angled up or down shots means gravity has less of an effect on the trajectory so the bullet strikes higher than you’d expect. Which means you aim low slightly low.Absolutely nobody. You're right. I doubt that was the issue here, and I don't think that @Quixote has said it was.
But shooting down hill, his point of aim on the body of the deer should certainly have been higher than it would have been on the flat, in order to allow for the angle at which the bullet was passing through the animal.
But, for the shot described, aiming at your normal aim point, would mean the impact point would result in a quickly dead deer.

