They probably knew citizens and media would be photographing and filming them, most likely to avoid leaking the full costume.
Then again, this isn't time this has happened on a Batman set.
"The MSM is a general purpose 2D camera. It’s a larger evolution of the MKII design (loaded with a 1000 foot magazine here), with a more elegant internal design and upgraded electronics like video output. You may know it as the camera that shot the famous Dark Knight Tumbler sequence…before it was destroyed by a stunt vehicle. Mike Hendriks had to repair the system as it’s but one of four such cameras in the world. (I overheard that while it’s insured for $500,000, repairs came in at well under half that.)"