Mr March:
I don't think that's the case...
Theory 1: Molten Core Exploded into space: Again, space, while cold, does not have much (any) ability to conduct heat. Thus, if the molten core had exploded into space, there should still have been visible the molten bubble of the core as it catastrophically escaped the core. However, given enormous size of the cavity caused by the DE, I doubt such an explosion would have taken place.
Theory 2: Dimensioin Eater pulled in the core: The first reason is "in unvierse", the only other example of a spherical fold phenomena was the SDF-1's initial jump from the Earth. In that case, the fold bubble was surrounded by a much less viscous and dense fluid (water) which wasn't drawn up into the fold bubble. Instead, the fold bubble merely ported away what was already in the confines of the bubble. From that, I think we can assume that fold phenomena does not have the ability to pull in nearby matter.
Theory 3: This goes to the intent of the animation. While the idea of the cavity from the removed core is plausible, from the visuals shown, I think we can assume that the animators intended to illustrate that the DE created a spherical fold bubble. The edges are too clean and there's a complete lack of deformation or debris.
Also, there's no reason to assume that even if the core were molten, it would spew out in giant ribbons. The core would still be incredibly dense gravity would still be in effect, it would WANT to stay together and not fling itself out into space. If anything, given enough time, gravity and the forces of erosion would eventually pull the planet back into a spherical shape. Remember, Gallia 4 wasn't hit by some huge mass, there's no force that cracked the cust or would have caused ejecta of any sort.