I'm surprised you even hit the fox. Slowed right down and paused at the split second where the shot was released, the crosshairs were not even on the vitals of the fox. Which suggests to me that this bullet came apart prior to hitting the target and tumbled in your favour, went high and hit the fox fatally. Had the bullet held together and performed properly (assuming your rifle is not zeroed 4-5 inches high) then i suspect you would have hit the inside of the fox's right foreleg or even below the brisket area. I might be wrong but it looked a poor shot yet the animal fell straight over. Something odd is going on there.