When you have been given the right to kill people without legal consequence, the distinction become rather hard to make. There have been a lot of unwarranted killings by police that seem to have gone unpunished, how do you chalk those up?
If the goal is to make a factual argument, then the facts are that the # of police murders is less than the # of police killings, because some portion of those killings are justifiable.
Where we draw the line is debatable, but the person you were responding to wasn't really attempting to draw a line.