Sure thing.
First of all, you gather a group of like-minded people together, and develop a Plan. The actual participants do not all have to come from the same shard, even (though apparently they did, in this particular case) Then you determine which shard you wish to 'visit' en masse, and everyone generates a newbie character on the shard to be 'visited', generally at the same Inn. Sometimes, you can have local, veteran cohorts who will equip yer newbie selves, but more often, the fun lies in the fact that you have NOTHING to lose...no possessions, nor fame, nor glory (well, maybe dignity, but then you're basically anonymous anyway)
Sometimes, such invasions can be mean-spirited and spiteful, but those are the exceptions in my experience. Usually they are just semi-hilarious, free-spirited fun. Sometimes, they are planned for weeks, and involve training up all the newbies in their spare time, in preparation for the 'event', with storylines written up and many consultations beforehand. It varies, depending on your group and what their basic goal may be.