In all honesty, my cp and I had a similar conversation in the recent past, which was heard by other people that looked at me like I was crazy. However, what wasn't heard was the fact that she and I have talked about eating healthful foods, and as much of that as she could possibly want, avoiding fast food (competition concessions count,) taking care of her heart health - and this includes maintaining a healthy weight.
You see, Paparazzi had a massive heart attack a couple of weeks ago. Part of reason for 100% blockage in his right coronary artery was from eating fatty foods and not watching his weight. He's not morbidly obese or anything, and he's only 36 years old, so it was a big wake-up call for us.
Maybe the parent you witnessed was insensitive, or flat-out wrong, but maybe there were additional reasons for her reaction.