Orcs expects the smaller greenskins to run away and it doesn't really surprise them when they do. The sight of fleeing Gobbos and Snotlings simply reminds the bigger and bolder Orcs why they are best. Consequently, when a Goblin unit, Snotling Swarm or Snotling Pump Wagon is destroyed, breaks or flees past, Orc units do not need to test for panic. See Warhammer rulebook for the complete Panic rules, pages 80-81. [p. 6 of AB]