He was drunk and frustrated. He was likely kicking the base of the door trying to be loud enough to wake a roommate to open the door since he couldn’t get his key to work and was confused. Castle doctrine should not have applied here as he was likely not an obvious threat. The shooter could probably have talked with him through the door or, heaven forbid, actually opened the door and talked with him to figure out what was going on and helped the obviously inebriated young man home.
Castle doctrine is intended for when someone is making an obvious threat with deadly intent. The way it is being implemented here you can shoot a proselytizing baptist dead on your porch because they were there to attack your soul.