I think it's safe to assume he wasn't trying to encounter the home owner.
Without using any hindsight whatsoever, let's assume something a little different and see how it plays out, shall we?
Let's assume the kid knocked on the front door and let's assume he did have a weapon. Let's assume the kid's intention was, if the door was opened by the occupant of the house, to immediately force the door open, threaten the occupant of the house with the weapon, and complete the robbery, possibly by signaling others in waiting to help him rob the place.
Now, thinking nobody was at home, he goes to the back door to enter the house with less likelihood of being noticed. Mr. Homeowner calls out to the kid to go away, and now the kid switches back to his original plan in the paragraph above and produces a weapon and decides to enter the house with the weapon.
Keep in mind that the homeowner had no hindsight when the invasion was occurring. Since the homeowner can only go on assumptions during the time when the incident is occurring, which do you think was a safer course of action for the homeowner to take?
You know, it was by ASSuming that the kid got himself shot.
And, btw, I am only using the word kid out of consideration, I still think he was a criminal, nothing more, nothing less.
The only think Mr. Homeowner did was to not ASSume anything, and to take the steps needed to ensure his greatest chances of not being harmed by a criminal.