No, I'm quite sure Hannibal DID order his Iberian mercenaries to feign retreat. He did this so that the romans would advance, and make the whole ordeal so much easier for his troops to envelop the romans. This was, of course, succesfull, and he didn't have to loose as many troops as he might have done otherwise.
EDIT:
http://www.roman-empire.net/army/cannae.html
"The crescent of Celtic and Spanish swordsmen buckled and retreated. To the Romans this appeared to be due to their powerful drive into the opponents lines. In fact the troops had been told to retreat."
Bookmarks