I see one hit just in front of the flap. This would be called a snap shot. With the rate of fire of the LA cannons, and the speed of the P51, he was lucky to have one round hit.
I am not positive, but I believe the structural part of the wing is a bit more forward on the wing. But this is a game, and the magic spot was not hit

Looks like the P51 driver was lucky, but by no way is this a for sure kill shot. A better shot would have been a tracking shot behind the P51. Tracking shots have a better chance of getting more then one cannon rounds into the target.
When you go for the snap shot, you give up angles. This is called an overshoot. If you miss, you just gave your enemy a opportunity to get a better shot at you. It looks like this P51 driver took advantage of it

Find a good trainer. They can show you why this happens, and how to set up for a better shot.
Gunner