Line of sight from the hotel to the concert is 1300 feet horizontally and 320 feet vertically - or a 4 to 1 ratio. Inside the hotel room it is 36 inches horizontally from the muzzle to the window and 9 inches vertically from the muzzle to the carpet - or a 4 to 1 ratio. Try to picture it in your mind - two triangles both with the same ratios of horizontal to vertical legs - now do you think the third legs of the triangles (the hypotenuses) would be at the same angle?
Regardless of the angle of the dangle, shooter needs to get the muzzle out of the vertical plane of the wall/window sill. In doing so, he is a target, he is not back in the room, and thus can be shot and hit.
Arguing will not change that, nor will angles and hypotenuses and other bullshit.