Those marks look typical of using a machine driven cutter possibly with a follower to keep it central and cutting swarf has worked its way in between the barrel walls and the follower or the cutter itself. Also it could be a case of insufficient coolant/lubricant flow to clear the cutting swarf, so it gets trapped. A blunt cutter though this should never be the case at all if the person is a careful craftsman or woman. Those marks are the best argument for using a reamer by hand with lots of cutting oil and above all taking your time.
