Cardiologist here :D
The vast majority of my time is spent looking after people who smoke, and the people who have first degree relatives with heart disease (eg parents, siblings etc).
There is always the odd person who seems to lead a blameless lifestyle and doesn’t have a family history who pops up in my clinics/ward from time to time. But they are in the absolute minority.
There is some evidence that very strenuous exercise can precipitate something happening eg an MI, but this happens in people in whom it would have happened anyway at some point. Anecdotally, there always seems to be a peak of heart attacks when it’s snowy and all the old guys go out to clear their drives of snow with a shovel (having not been accustomed to that sort of exertion, on a background of smoking etc).
Regular cardiovascular exercise is good for you. I agree with paulatmtbleasing’s thoughts that maybe your friend just doesn’t want to get out there and exercise.