Your friend seems to have had a sudden death (witnessed death within 1 hour of becoming sick). The commonest cause is a malignant ventricular arrhythmias (sudden accelaration of the rate of pumping chamber, making it beat chaotically). The important causes for this catastrophe are coronary artery disease, cardiomyopathy (primary disease of heart muscle), and some unusual causes like long QT syndrome (an ECG abnormality since birth).
Alcohol taken a night before the mishap seems to be only coincidental. However, alcohol in a very high dose can also precipitate a rhythm disorder which can be fatal. Invariably such individuals have an underlying heart disease. Adulterated alcohol with methyl alcohol can also cause death. However, since no other person who took the same drink had an adverse outcome this cause seems less likely.
The indigestion like symptoms in this case could be due to reduction of blood supply to the undersurface of the heart (inferior wall) as a consequence of fat deposition in the right coronary artery (atheroscerotic heart disease). The fatal outcome could be due to a heart attack. We do see such attacks in young people in our mileau often these days.
The final answer of the cause of death could only be ascertained by an autopsy which should always be encouraged in such cases.