Sounds like great work.
My mind boggles whenever I read something like:
It just doesn't seem feasible. Can you expand on how exactly he managed to get such huge damage?
That's not hard at all to achieve for a striker. Try a Holy Avenger, critting on 19-20, with 2 rending axe's and Two-weapon Fighting and Opening. Take Eternal Seeker at Epic, drop in a few points to Strength to boost your attack and the round before use something like Bond Of Justice, then use Hurricane Of Blades on a single target. Have Punishing Radiance, Font of Radiance and Justice Hammer for feats. Use Assault boots, Symbol Of Divine Light.
With any luck at all, you will crit. When you do, you get extra attacks from TWO and Rending. More chances to crit again. Target is knocked down, probably dazed, vulnerable to Radiant, blah, blah blah.. Literally hundreds of points of damage is routinely done with this combination.
If you've got Divine Mastery and Epic Resurgence, you can do this attack *twice* per encounter.