You said you "one shot" Belial. "Oneshotting" in games generally means just that; one shot, one kill, as in your barbarian hit Belial once and Belial died. Hence, if your barbarian had 8K DPS, Belial would've had similar health. You used the term to state that you killed Belial on your first try, which is where the confusion arose from, albeit "oneshotting" has been used similarly before.
As for killing Belial with 8K DPS on a barbarian, that's not too shabby, seeing as though you yourself most likely get "twoshot" by his punches even with those stats. How many bombardments did he do? Must've done at least two, if not three. Anyway, well done with those stats.