Although, you are correct that in terms of absolute numbers he does not dispute that World War II had the highest number of deaths and casualties. That is not in dispute by anyone. What he strongly maintains is that steadily the percentage of the population that dies at the hands of other people has steadily decreased - even in spite of massive atrocities such as the two great wars of the 20th century. Based on forensic archeology and also comparisons with recently existing or currently existing non-state hunter-gatherer societies - the percentage of death by some form of homicide averages around 15% but goes as high as more than 50% . Life in early state societies or medieval society had a percentage averaging around 10% based on the consensus of the best evidence available. Globally in the 20th century it is reasonably estimated that about 3% of the population died as a result of acts of violence. Post World War II and Now post cold-war the percentage is well bellow 1% globally.
He does measure specific acts of physical violence - with a concentration on homicides. Certainly my experience with the third world where I have spent most of my life, I have found that when it comes to working 12 hour shifts in Nike factories - no one has to burn anyone's village down to find workers. As low as their wages may be and as harsh as their conditions are - the realities of the alternative and the hopes for earning some money as opposed to little or no money insures that the Nike factories of the world have several times more applicants then they have positions. Thats just how things are in most of the world - harsh but still a lot less harsh than a world where torturing people to death was sanctioned by church authority and regarded as good, clean and moral entertainment - a world where the possibility of a roaming hoards burning down the village, killing all the men, raping all the women and selling the children into chattel slavery. That world which sounds like a nightmare to our delicate 21st century sensibilities was only a few centuries ago the world of our European ancestors - and the world just about everywhere else was many times even worse.