Couple things.
What type of packaging was the rifle in?
Why did be take it out of the packaging and move to a different section of the store?
All of the Walmarts around have here a separate register In sporting goods around here.
If you are interested in the weapon you look at it there, put it back in the box, buy it or not. You don't keep it and go try on pants.
If he had stayed in sporting goods this probably wouldn't have happened.
Why was he acting so bizzare?
He may have been trolling for a reaction.
Keep in mind that we are in a state of heightened awareness due to muslims. I expect to hear of a mass terrorist shooting in, say, a department store or some other public place any day.
The cops would have no idea that it wasn't loaded. If he wanted to he could have had it loaded and charged in seconds.
In context, it was stupid, but not criminal.i doubt it was packaged at all. Many air rifles are simply sold off the shelf.
He was on the phone and was not paying attention and certainly not looking for a reaction. I doubt he thought about anything at all before the cop shot him.