What makes pneumonia not an interstitial lung disease?

They are different: A pneumonia is caused by an organism causing destruction of the lung tissue. Interstitial lung disease is inflammation of the lung and usually starts in the "interstitium" but later can involve other parts of the lung. But, one is felt to be an infection, while the other is more"immune" caused. The picture is of a pneumonia in the left of the picture(all the white area compared to the dark).