Yeah, a Horde Kobold isn't 3 kobolds in a square, it's a single kobold meant to be casually dispatched while fighting a larger number of total enemies for three purposes:
1) To look cool.
2) To soak up attacks that would otherwise hit a more important target (making them live longer)
3) For AoE spells and effects to have a bigger 'mechanical' impact by hitting more squares full of enemies and probably wiping them off the battlefield en masse.
Because it kind of feels awesome to wipe out 12 people with a Fireball even if you're still fighting several "Lieutenants" and the BBEG.
They've still got enough teeth to bite, though, to ensure they're still a threat.