Seeing a big, tall man standing on the railing (as opposed to someone holding a little child up to see better) would signal to me, if I were inside the enclosure, “uh-oh, someone’s coming in!”
That’s definitely threatening enough to provoke an aggressive response - and a result that had never been provoked before in 67 years there, and never anywhere else at any zoo in the U.S.
Police say the taunting "contributed" to the attack.