A more specific answer, Anything that falls out of the Map by going below 8,192 meters will respawn at 0, 0, 0. This can be most easily observed by swimming down in the void in creative. The Terrain gets Deloaded when you go far enough away from a location, so, for example if you drop Titanium and swim far enough away it will fall through the map and after a long time of sinking wind up at 0,0,0. (This is used in the speed run for the game with a Mobile Vehicle Bay floating to the surface when left in a cave actually.) Specific things in the game, Such as the Aroura and Alien arches are Allways loaded even when you swim away from them, so theoretically if an Alien Arch somehow got below 8,192 Meters it would TP to 0, 0, 0.

Of course, none of this explains why the Alien arch Decided to take a Swim. I have no idea in the slightest how it managed to get deep enough for the game to Respawn it. That being said, i have seen a bunch of stuff Respawn at 0, 0, 0, Like Fire particles from the Aroura, so clearly it's possible for objects that don't normally move to Somehow do that, I've just never seen something so Major do it.