This estimate probably includes the deaths of people caused indirectly by war, like infrastructure destruction, healthcare facilities destruction, depleted uranium, contaminated water, contaminated farmland, unexploded ordinance, diseases that arise from lack of sanitation, starvation... And so on and so forth. I bet you can even remember a few more than those I enumerated. Maybe some would like to consider these as "externalities" for the overall cost of any given war.
