Maybe the old man was just clowning around, but who knows. And anyway that's NOT the time or place for the old man to be fooling around.
His hand was at chest level. Last I remember, police carry at the hip. That wasn't a tiny shove, it was hard enough to cause the man to stumble backwards, falling and hitting his head on the concrete, causing him to start bleeding out of his ear. Those blue thugs are throwing a temper tantrum because the one that did the shoving was being punished.