I don't know if talking to the npc was necessary, but there was a pretty large battle that followed and I thought it was pretty cool.
It is if you want rewards, but the NPCs show up regardless of whether you join the fight (Unlike levequests where the enemies/NPCs don't exist unless you're on the quest) The only real defect in this event is that if no players are involved, the enemies just wait around. They should add some NPC fighters or something so that it looks more active.