The grandparent comment didn't mention vegetables or portion control, which I'm sure the grandparent knew but it's fine to emphasize it. I think the parent comment to yours is fine, just re-emphasizing key points that the parent didn't explicitly state.
Yes, and the doctors and nutritionists he talks about probably didn't know about these incredibly basic concepts either? You might not know this but nutritionists are professionals who give people advice about healthy diets.
