Um, no, it isn't. The likelyhood of an armed citizen defending him/herself in Richmond is not the same as the likelyhood of someone going out and murdering someone and then planting the rifle/taped magazine that they carry around as a "throw gun" just in case they want to murder someone.
You're probably right about that.
But until there's some more investigation, it doesn't rule out some scenario such as the kid's riding around with his unloaded, duct-taped rifle, and cuts off the driver. The driver and the kid exchange words, tensions escalate, kid gets shot.
Driver realizes what he's done and spins a tale.
If the kid was threatening the guy then he got what was coming to him. The article doesn't give that much information.