One of the new characters to D&D forth edition is the Dragonborn - a humanoid dragon with the ability to use dragon breath. They can have one of several different types of breath weapons, Zetork's happens to be lightning.
Using the breath weapon is only a minor action, so Zetork was able to move and attack on the same turn. Taddin moved into flank so that the rogue could get combat advantage over the Kobold. Besides the normal +2 to hit, rogues do extra damage to a flanked opponent.
The Kobold Wyrmpriest also has dragon related abilities. In the last he is shown throwing a globe of fire. He will be using other powers as the combat progresses.
I should note that the group of Kobolds behind the party contained three minons and a skirmisher. Minons die whenever they take damage and that's why only the skirmisher survived the blast.