A few things... I am into guns. I'm an Okie, it's a huge part of Southern Oklahoma culture. We hunt, we fish, etc. We are raised around guns and are taught at an early age how to be safe around them.
Sure, it takes some practice... but I can take anyone on this page and teach them to make that shot in a very short period of time. It's not hard. Your heartrate and breathing are massive when it comes to long range shots. But the thing is... this isn't long range. It's sub-200 yards. That's an EASY shot. The 30-06 round itself is extremely fast and extremely accurate. If you have your weapon zeroed at 100 yards (some hunters do it at 200), this round has a drop of about 3". Meaning, you aim at someone's head... you'll likely hit him in the jaw/neck. This killer likely missed his aim-point.
And yes, it's CLEAR this kid was raised around firearms. It's Utah... much like Oklahoma, Texas, Arkansas, Louisiana, etc. people are raised around them. There are photos of he and his brothers with firearms. Recently, his mother posted a photo of her other son (Austin) with a 'tricked out' Ruger 10-22 at a range. The weapon you really start shooting as a kid. No one ever said he put a rifle together real quick and decided to take this shot. He clearly had some practice/understanding. But what I'm saying, I can take YOU or anyone here and teach you to reach out to a human size target at 500 yards in about an hour with a decent set-up.
PS: Not a 'redneck'. I have a masters degree and work as a mental health professional. I'm far from "unsophisticated", which is a key trait to the term 'redneck'. My father is a doctor, mother is a BS RN. My grandfather was a chemical engineer for Phillips 66 and holds 27 patients. My uncle was a literal 'rocket scientist' for NASA.