While I didn't see the video and am unable to comment on the discussion or your form this image comes to mind:
20160302_600.jpg
So as the barbell gets heavier the COM of the barbell lifter system moves up. There will be a slight angle to the torso as a result of this. That said I have seen plenty of people over do this or round their upper back. Again not sure what the conversation was in reference to but the image above should clarify.