As I said, they're supposed to use the first frame available to them in which the ball has been clearly played. So I don't know why you're saying the bold as if you didn't expect to see the ball having been played in the frame they used. There is indeed room for difference between that frame and the hypothetical perfect frame that would exist if the camera framerate was better, which is why they have the MOE Garnacho fell outside. You can feel free to complain that the MOE doesn't sufficiently compensate for the gap in frames if you want, but it is what it is. Until the tech improves, they can only work with the frames and MOE at their disposal, which they did.
And they didn't use the wrong part of the body. The defender's shoulder was further forward than his head because his upper body was turned. Again, that's something they're able to easily determine with the scope lines they use, and in this case I thought it was pretty clear just from looking at the image. Though given at least one poster tried to tell me it was physically impossible to have your shoulder further forward than your head, I'm not surprised there's an unwillingness to accept that.
There was no conspiracy or error in that offside call. You don't have to like it, you might think there is room for error in the system, but it was completely consistent with how offsides are supposed to be applied. In fact we've had much tighter calls than that go against us in the past.