The solar systems had plenty of debris (still does) and that affected the surface of the moon greatly.  This is the time frame in their models where many of these major impacts took place:

Around 4.3 billion years ago, a giant impact battered the moon’s south pole, sending debris as far as the opposite side of the moon. The impact formed the Aitken basin. At roughly 2,500 kilometers in diameter and 13 kilometers deep, it is one of the largest known impact craters in the Solar System.

Its formation marked the beginning of a period of large-scale changes to the moon’s surface. Over several hundred million years, the lunar terrain was rocked by a succession of heavy impacts. Some formed large basins that would eventually fill in to become the dark colored patches of the moon known as maria.

These impacts punched enormous holes in the relatively thin lunar crust. Because the moon had not yet fully cooled on the inside, lava began to seep out through cracks opened up by the impacts.

We hope you enjoy the video.  Feel free to comment on any other theories you might have!