The event only happened once as far as i know but many people exploited one thing that anet didn't think well enough. The exploit is related to the fact that the final chest is not like those at the dragons where it only spanws for you if you get credit for the mission. Instead they designed it like those permanent chest that you can loot once a day and that are ussually guarded by a veteran or champion that you have to kill or else they don't give you enough time to channel the open command that is required.
Perhaps they did it this way to ensure everybody to get a chest even you arrived late or something, but this brought up the exploit:
With an event with so many people, the event itself was played in many overflow servers. So people ussually played on their overflow server and thep kept moving to a different overflow to have a chance to loot another chest. It was really very easy. You only needed to keep looking at your guild chat to see when your guildmates just ended the mission, form a party with them and then join them in their overflow for a new chest to loot.
As i'm from Europe and the event itself took several hours i went to sleep as soon as i finished and this morning i learnt about this.
And what's the problem you may ask? Well, that was a chest that you were supposed to open only once and i know of people who looted it up to 5-6 times by changing servers.
And a worse problem. When anet learnt about this they abruptly ended the event by releasing a new build with no more chances to start the event. That made many people lose the chance to open the chest as they were disconnected in the middle. Of course, i'm specially talking about people in asian countries or ausies who due to being in a different time zone there were few people there at those early hours, so the event dragged on for much longer until people started connecting. Anet says they are going to compensate these people, but i ignore how.