When a resident slammed the door on the officer, it apparently caught the officer's hand. With his free hand, he reached for his gun and opened fire into the closed door. There were nine people in the home.
Yes, the house apparently has a reputation as being a "drug house." But there are a couple of issues here.
First, that the officer's hand was caught in the door at least suggests that he was attempting to enter the house. It is unclear from the story whether he had a warrant. A police officer can enter a home without a warrant under extreme, "exigent circumstances," such as the belief that someone is in the process of committing a violent crime. A secondhand tip that someone in a residence might be ingesting illegal drugs is not an exigent circumstance.
Second, even if the officer wasn't trying to enter the home, he obviously had positioned himself in a way that prevented the residents from declining a search and closing the door. The article implies that the residents intentionally tried to slam the door so that it would injure the officer's hand. Even if that were the case, it doesn't justify blindly firing into a closed door while unaware of what is on the other side.