if you look at the moment it touched the ground, i think it is in. in the first picture the ball was shown just after it touched the ground. look at balls shape. it is not even deformed. it is perfect circle. i think there is nothing wrong with challenge system.
maybe if we were talking about millimeters but there is a huge difference between those two pics. the animation even shows part of the ball was inside the court and not even on the line. to me noway that's possible.
and actually I even think in the first picture the ball is showing just "before" it touches the ground. before or after, it still has contact with the ground.
I simply think showing the real picture is better. I just don't trust this system. I had seen such mistakes before.