Don't be ridiculous. When you warp the actual truth, it's easy to tell a story that makes the cops look bad. It's always the same with you propagandists.
The acorn did not fall on "the ground". The acorn fell onto the roof of his squad car. This is an important detail because the speed and angle at which the acorn would have hit the metal of the car perfectly replicated the sound of a previously searched and handcuffed criminal in his back seat freeing himself, locating his expertly hidden firearm, and firing it through glass at the officer.
Really, it's a mistake that any reasonable, level headed person could make.