The Trolley scenario situation is different because it is trying to make a choice for the action that is less evil. In comparison, this person who has the five organs is healthy and not in the same situation as the people. This is not to say that some lives are important than others based on their health or their specific situation. More specifically, I think this healthy donor situation brings in another factor which is a person who is not tied to the railroad tracks. The trolley scenario has people in the same situation. It becomes more difficult when you have to compare lives in different situations.
By bringing in this healthy person, there is a new situation that is created. Even though more lives may be saved, this will sacrifice the happiness of one other person, which cannot be easily compared across lives. More importantly, this new situation brings in the factor of consent. If the healthy person is willing to give his organs to the 5 people, then the situation is more understandable. However, if this person does not give their consent than the perspective of one or a few other people is not enough to choose and limit the happiness and well-being of this healthy person.