I also agree with comments above.
It's nice that you have him lined up with that big fence post in your neighbors yard because it gives you a good visual marker in the video of where your son is releasing the ball. If you'll notice in the slo-mo video - he releases the ball right at the fence post. Release should be happening out in front of that fence post - or out in front of his head/front knee. The reason he is releasing so far back is due to his leaning to his glove side. Instead of his body pulling him to that side, he needs to keep his head level and project that force forward to the plate.