Champion of the council
After talking to him or her, cant remember in the pavillion continue to kill mobs in the pavillion. Easiest way.
The only way I got any credit for that one was by fighting in the pavillion while representing Lion’s Arch.
You don’t get any credit for it doing any balloon events as far as I could tell. (and I had to do almost all of them, since it didn’t give me credit for the first several towers I climbed.)