I am a pretty old guy and I don't know anyone who said or thought that, 2 seconds of HD viewing can prove it ridiculously false. to the point that viewing TV is a fundamentally different process. Baseball and Hockey on HD is transformational, you aren't picking up any small details in the good old days.
Size may better point, spreading the same pixels over a larger area means they are bigger, and depending on the viewing distance absolutely *does* make a difference, you do not need a study to tell you that. That is where the 4K or 8K *does* make a difference. What they are saying, really, is the same thing that Apple figured out long ago - the pixel dimensions at the viewing distance only has to be smaller than a cone or rod cell in your retina, that is the limit beyond which is it no longer important..