Remnants of Theia, an ancient planet that collided with the Earth
cnn.com
cnn.com
Maybe the Earth was hot enough to kind of re-melt the proto-moon as it careened away, sort of repairing it, like two separating droplets of liquid.
Anything in space that is sufficiently large will become a sphere, because gravity, and the moon is sufficiently large.
Combined with the idea that different minerals can be formed from the same rock-stuff under the Earth's crust when it's hot enough, I see how there's a clear mixing of Very Hot Material.
As it cools, maybe enough bulk is re-incorporated together to become those blobs--Large, Low-Velocity Provinces (LLVP)--that were detected.