Infernal Expansion is a mod in the nether that adds a variety of things, one of which being structures. Some structures, such as the Bastion Outpost, Strider Altar and GSC ruins structures have chests that will open with the corresponding loot table outside of Crucial 2. However, opening a IE structure chest in C2 will cause the game to register various different loot tables from other structures, such as mineshafts, sunken ships and villages.

All you need to do to encounter this bug is enter the nether and open a chest that generates from a random Infernal Expansion structure.