Killing players while they are flying yields no items upon death

My friend had my items in his inventory when he killed me and he said he was going to give them back, I managed to get a sword to kill HIM and get the stuff he took instantly... None of the stuff dropped, only a few things did drop. All I saw was an elytra which was on him as he just pressed A in mid air and he died. The sword had fire aspect, so that might be a factor but I'm not sure...