i'm not sure narrowed coronary arteries would show up with a regular physical and blood pressure test. (as it's not systemic) perhaps someone with more medical knowledge might speak up.
But, to test for coronary artery blockage would take a very specific test. (i think they can do spectography, or ct, or angiography)
I can see how this might be overlooked - If he wasn't experiencing "classical" angina symptoms, may not have a family history of heart disease, and otherwise 'looks' healthy.......
i mean it's knowledge too.. maybe what you and i have knowledge to look for this kind of problem or even be aware. maybe he wasn't.
still it's very sad that this happened - esp at his young age.