None of us can possibly infer from that photo the circumstances of what happened. Were they really rolling down the streets in armored vehicles pointing guns in every window? You're creating a narrative and inventing a story to fill in the gaps of what the photo is incapable of showing. And then getting all worked up about the story.
Since no one bothered to answer my last question, I'll ask another - is there any circumstance under which you would consider that cop justified in bringing his weapon up on the person in the window? If your answer is yes, without knowing for certain that wasn't what happened, you're simply reacting emotionally, and in the absence of facts.
Perhaps the photographer was one of those cop-block type ********, someone who intentionally instigates an incident with law enforcement to capture their reaction on camera, and then misrepresent the circumstances to make them look bad. The photographer could have threw the curtains open suddenly, knowing the cop would be startled and react. We simply don't know.
Locking down the city was a mistake. More terrorist plots have been foiled since 9/11 as the result of citizen involvement than by law enforcement. We the People are the dept. of homeland security, and it's about time that our politicians in office and administrators with a badge start recognizing it.