No it doesn't generate clumps. In 3 for loops (x, y, z) it checks if the block is air, if the block bellow is solid and then it uses CubicNoise1D to decide if there should be a mushroom/fire.
I uploaded it to a new branch: https://github.com/mc-server/MCServer/tree/NetherFinish
I uploaded it to a new branch: https://github.com/mc-server/MCServer/tree/NetherFinish