And on top of all of that, player disputes of a personal nature like this aren't really handled here in the Reports and Grievances... This sort of bickering about fight rules is sort of pointless, since in the end the only rules that apply in the Arena are the ones that both players actually follow, not necessarily what they agree to.
While it may not have been very sportsmanlike of him to do what he did, he killed you in an area where there are no holds barred, and any combatants are permitted to arrange rules of their own to follow themselves.
Unless a mod really feels the need to step in and restore his stuff, I can't imagine this will really be reversed. The risk of the PVP arena is that you may lose your stuff.
Topic Locked, pending further intervention by any mod who feels it necessary.