Why doesn’t CMB heat up Boomerang Nebula ? I was listening to this documentary and learned that Boomerang is cooler than CMB. How could that be? Is it constantly being cooled by escaping gas from its binary star that keeps temperature lower than CMB or is there something else at play here?

Based on my research, I understand that Boomerang nebula is the coldest place in the universe because the rate at which its dying star is ejecting the material is 10x what you would normally expect, leading to adiabatic cooling. So, it could be this extraordinary ejection rate that is cooling the nebula faster than CMB can heat it. But could it also be that the nebula is somehow insulated from CMB or any other explanations?