Here is a much better description of the event, from a real news source:
Surveillance Video Captured Deadly Robbery at a Lamont Gas Station
A couple facts from the story:
The shop owner fired first.
There was an exchange of gunfire.
I can't find an article anywhere, except the one posted by the OP, that suggests the victim was carrying with an empty chamber. I will agree that he appears to work the slide upon drawing, although I've seen nothing to suggest the reason for doing so. It is possible that he was working the slide because he was unfamiliar with operation of the pistol, and it is also possible that he was carrying on an empty chamber. To me, this video suggests that one should be familiar with the operation of one's pistol, and nothing more.
Condolences to the family.