I cannot be sure this is what happened but one scenario is that aspergillus can grow very slowly and almost without symptoms to form a ball of fungus in vulnerable areas of the lung. As we age we are more vulnerable to all types of infection so your fathers age may have contributed. These fungal balls can be very difficult to spot.

If a ball (aspergilloma) happens close to a major blood vessel then there can be sudden episodes of bleeding that need immediate medical attention. Patients will lose blood via their mouths as the bleeding is in their lungs - this would explain the location and amount of blood you saw. It sounds like your father was unlucky to have had an infection so close to one of his blood vessels that the first time he had a bleed it was severe - usually we see little bits of blood coming up after coughing and that acts as a warning.

We need better methods of diagnosis of these infections to avoid people dying like this - our current methods rely on quite specialised skills and as these infections are rare not many doctors will be experienced at identifying aspergilloma. There are some kits becoming available but more research is needed.