I'm missing where Mr. Todd Scott was in the liquor store at the time the gunman entered and began shooting, as well as when he returned fire. Maybe it's just not captured from the video camera angel shown?
I'm not a tactical expert but it does appear that the shooter was not just randomly coming around the corner. It also appears to me that the shots at the already-fleeing customers may have been to convince them to stay out of the way. The person behind the counter does seem to be the primary target.
If nothing else the video shows how quickly things happen and how little time one has to assess, decide to act, formulate a plan, and then carry it out.