There was almost certainly drugs or some sort of heart condition involved. Unfortunately, congenital defects can go unnoticed until circumstances like these.

The idea that three long days, alone, is what killed him is ridiculous. Going a few days with just a couple of hours of sleep a night is something many people do at points in their lives (e.g. working parents with small children when they get sick). And the "100 hour" weeks mentioned in the article are stressful, but again, nothing a working mom (or dad!) with a baby hasn't experienced.