There are so many things in here as far as tactics...
Having visibility to the area around your entranceway
Having a secondary door like a security storm door
Not opening a door when something is suspect - like not being able to see who is there, or something odd about the situation.
There are a lot of points, but the one that sticks out for me is that opening a door with a long gun is pretty tricky. Most long guns are deployed with two hands. Despite all the other things listed above, it would have been a lot easier for him to respond with a handgun.
The fact that the resident got pushed to the wall indicates to me that the intruder was close enough to grab the rifle... he just failed to.