Final answer:
David had a neurological disorder related to an undetected Hodgkin's lymphoma that affected his short-term memory and was likely exacerbated by his compromised immune system due to medication for Crohn's disease.
Step-by-step explanation:
David experienced a neurological disorder due to an undiscovered mass in his mediastinum region, diagnosed as Hodgkin's lymphoma. This cancer likely caused antibodies to attack the nervous system, affecting his memory. The regions of the brain that were probably affected by the antibodies are the hippocampus and other associated structures involved in forming new memories, indicating that the type of memory impacted was short-term memory.
Additionally, David's exposure to bird droppings could have made him susceptible to cryptococcal meningitis, especially since he was taking anti-inflammatory medication for Crohn's disease, which may have compromised his immune system.