This is an extreme hills biome which has all the ingredients which usually makes it a savanna biome. It has all those savanna trees, but the biome painting is greener and in that sense it doesn’t look like normal savanna. This means it’s basically a fake savanna biome posing as a real one. However, it’s probably more likely caused by a bug in the system than by an intelligent pig AI gone rogue in the world.
Found by: MeowKitty