A more informative article from the L.A. Daily News. FTA:
The clerk shot the guy with the gun, stopped shooting him when he wasn’t a threat anymore, and didn’t shoot anyone else. Better than the cops do, frankly.
Really, the fact the criminals were robbing—taking money or goods in the possession of another, from his or her person or immediate presence, by force or intimidation—should be sufficient. OTOH, the media is frequently imprecise with their descriptive language, and it wouldn’t be surprising for them to call a mere theft a robbery.