It's a combination of two common 'trolley problem' moral dilemmas.

Do you pull the switch to kill fewer people, even though that would actively involve you in the decision to kill people?

AND

There is a trolley coming - you are with a heavy man on a bridge. Do you push the man off the bridge, knowing his body is substantial enough to gum up the trolley and stop it - to save a greater number of people?

In this scenario, by combining the two, pulling the lever will make the moral dilemma harder - because the fellow on the bridge must decide the life of 1 person vs. the life of 2. On the other hand, refusing to pull the lever will make the decision easier, if still not clear cut - as the fellow on the bridge must decide the life of 1 person vs. the life of 5.