Look at the bottom two pictures. Imagine the bolt starts to drop just as the floor of the elevator is at the same level as the observer's feet By the time the bolt hits the floor of the elevator, the floor will have moved upwards.
Imagine the observer has a large vertical ruler 3m long. He positions the top of the ruler at the height of the top of the elevator, when the elevator floor is at his feet. The bottom of the ruler, level with the floor of the elevator at the instant the bolt starts to drop, would be 3m below the top. Because the elevator is rising, by the time the bolt hits the elevator floor, the floor, and hence the bolt, will be at a level above the bottom of the ruler (which isn't in the elevator and so doesn't move). This means the ruler will measure a distance less than 3m for the drop.