Must be the nature, Original Dragon has Naive nature:
.iv = 255,
.lvl = 100,
.species = SPECIES_ORIGINAL_DRAGON,
.heldItem = ITEM_LUM_BERRY,
.evs = {0, 252, 0, 252, 6, 0},
.nature = NATURE_NAIVE,
.moves = {MOVE_DRAGON_RUSH, MOVE_BLUE_FLARE, MOVE_IRON_TAIL...