for starters, what "admin stuff"
how was he supposed to know
i think they were likely using slayer because it's dedicated, so why didn't he leave the minigame
Or, the infinitely easier solution of Admin-Orbing down below the terrain, dropping your body and going back into Admin Orb again.
Do your Admin stuff from there.
Then all you have to do is fly back up and respawn your body when you're done.
Or better yet, in your game mode based around killing and whatnot, don't just stop randomly on the street where someone in a car can get you.