Damage Control damage doesn't reset the damage you have done in previous bg's. Keep on doing Battlegrounds without logging or zoning and you'll get it.
I can tell you that you are FAR from the only one that got it - infact i got it myself after only 7 min in a wsg. And one of my guildes got it the same night in another wsg without being near the 300 k dmg or healing done..
Its a Shame if you want to try and get it later on :/