Batman made no move to surrender and clearly indicated as such. Given that *everyone* knows how well trained/skilled he is, how many damn weapons he carries, him not throwing himself to the ground with his hands up could easily be considered an aggressive move.
Police aren't required to wait for you to attack them before they can open fire. If they have reasonable cause to think you might attack, they can defend themselves. Given Batman's sheer number of consealed weapons, what happened here was common sense, not attempted murder.