http://wiki.guildwars2.com/wiki/Defend_the_reclaimed_camp_by_killing_centaurs
This is not a group event and a standard defend against the waves of enemies event.
Except, an absurd amount of centaurs will spawn much greater than a single person, or two people, hell a full party can deal with.
This is either bugged and all the waves spawn at once or well and truly overtuned.
Screenshot shows just two people doing the event.
