Final answer:
The patient's anemia is most likely caused by a surgical procedure, especially if it involved the surgical removal of part of the intestines or stomach which can lead to poor absorption of vitamin B12 and potential blood loss.
Step-by-step explanation:
The primary cause of the patient’s anemia is likely a surgical procedure. This is suggested by the information that pernicious anemia can result from poor absorption of vitamin B12, which is often seen in patients who have undergone surgical removal of part of their intestines or stomach, as sometimes occurs in weight-loss surgeries or treatments for severe intestinal disorders like Crohn's disease. Additionally, surgical interventions may cause blood loss anemias.