Usually when that happens you can run back and you're stuff is left on the ground as if you got your own kill, but everything is there (barrows items are broken) but if you where pking in void, firecape and so forth you'd be able to get those back as well. It's happened once or twice, it's common if you venge + brew and he attacks you, veng kills him and he killed you delaying the damage done to you till the eating delay is gone then it kills you giving you the kill. That might have been what happened.