[Warden Brows]

In Star Wars, the ability to produce artificial gravity and antigravity is well-established. It's a common feature in most Sci-Fi universes as well. The Interdictor cruiser works in this way, and this is of particular note because it's described as producing "Mass shadows" in hyperspace. Anything of sufficient mass will create a mass shadow in hyperspace, and this mass shadow CAN destroy objects that impact it. This is what Solo was referring to in Episode IV when he says "we could fly right through a star or bounce too close to a supernova. . ." Hyperspace is devoid of physical objects but items that produce enough gravity will manifest themselves as mass shadows.

Hyperdrives have a safety cutoff to prevent collisions with mass shadows, and this is how an Interdictor works, by triggering this cutoff with a focused gravity well in the path of an oncoming ship. Presumably the Mass Shadow Generator did more than that, and created real gravity that crushed the planet and pulled ships near the planet into it. Anything not close enough to be pulled in but not strong enough to escape is still trapped in the gravity well, relatively intact. The original technology may have been for an Interdictor type device (and may have been intended to keep the Mandalorians for escaping), hence the name, but that is not how it was used in this case.

Now, ignoring all these fantastic devices, there is one bit of physics that is quite correct: on the light side ending, you see the planet breaking up and rocks flying out into the ships. This is correct. Imagine twirling a rock on a string, and then cutting the string. The rock will fly out in a straight path. Add to this fact that objects closer to a mass orbit more quickly than objects farther away and you get the ultimate result: when the mass shadow generator's gravity field vanishes, objects closer to the planet fly out faster than objects farther away. This correct from a physics standpoint, and with nothing to restrain them, these objects will collide with slower-moving objects.