Bombers can miss if they make a major elevation change around the time they are dropping their bombs.
So if a bomber flies over the very high mountains of Astro Craters, its elevation climbs rapidly. While it's climbing up, if it tries to drop a bomb, it will undershoot (instead of dropping bombs that hit the target, it will drop bombs that land between the bomber and the target)
When a bomber leaves the very high mountains of Astro Craters, its elevation decreases rapidly. While elevation is decreasing, if it drops bombs, it is likely to overshoot the target (bombs don't hit the target, the target is between the bomber and the spot where the bombs land). This is what happened at about 18:30-19:00 in your game.
This is something that happens a lot on Astro Craters and on certain other maps. There are some parts of Point of Reach where a bomber can miss because it flies over mountains right before dropping bombs.
One way to get around this is if you ground-fire (tell the bombers to attack the ground). So if you're coming down from a mountain, you can tell the bombers to bomb the ground between the bomber and the ACU. Then when the bombs overshoot, they might hit the ACU.
Another way to get around this is to choose a different path. If you fly in through the "mouth" of Astro Craters, you avoid going over any mountains at all.
He could also have chosen a different target. For example, he could have crossed the mountains in the same place (at the bottom, the south part) but picked a different ACU to attack. If he flew over the enemy base and attacked the top ACU, the bombers would have fixed their elevation by the time they're ready to drop.
Changing the flight path can put you at risk of flak and other anti-air weapons, so it's not always the best option.
