There's no doubt. However, his point was still valid and you understood the point he was making. You just don’t feel comfortable with lay people, or commoners as you may prefer, making such comments.
Absolutely not. But I don't have an issue with you having an opinion nor making a statement based on that opinion or your life experience. And you have done just that...which is just fine.
If that opinion is 100% wrong and it's so ignorant that it's dangerous and irresponsible, I might tell you so (or I might ignore the ignorance???). That's not the case here. Advising people to eat right and exercise is not dangerous advice.
If he had said eat right, exercise and ignore your doctors advice if you're genetically predisposed to hypertension, that would have been dangerous advice.
You could have also agreed with his point and then added, "be careful if ______."
But that isn't what you did. I believe that I know why...but I'm not a trained psychologist so maybe I'm also FOS.