The questgiver for this PQ is almost impossible to find and when you do, he never stops. I have managed to get the quest ONE TIME only and only after hailing him no less than a dozen times just to get the quest window to pop up. Slow him down! Better yet, when the event spawns, just keep him in one spot! If you won't have him stand still, at least keep him up all the time running back and forth so if you miss him for the quest prior to the kill, you have it for the next time the event starts!
He does stop. After "a dark messenger" does his rounds telling the ballista workers to man their stations, he makes a full stop by the battlements. It's where I grab the quest and then fly/run over to the Iksar Hero spot. It's not convenient at all, but he does stop. Interesting that you were able to grab quest while he was running, I've tried and never could be fast enough. So that's good to know that it can happen.
fly low and fast to grab it while he is running. I'm at 175% air speed so I fly faster than he runs but not by much. Not that this is ideal mind. just a way to get the quest.
