I disagree with the person's belief that the lone skydiver must be lighter than the others simply because they are falling behind. The idea that heavier objects fall faster is a common misconception. In reality, all objects fall at the same rate when only gravity is acting on them, regardless of their mass. This is due to the principle of gravity: the acceleration due to gravity is approximately constant at around 9.8 meters per second squared for all objects near Earth's surface.
When a skydiver jumps out of a plane, they initially experience the force of gravity pulling them downward. While it is true that heavier objects experience a greater gravitational force (since weight is the product of mass and gravity), they also have more mass, which means that the increased force is balanced by the increased mass. As a result, the acceleration of all objects in free fall is the same, regardless of their weight. This principle was famously demonstrated by Galileo's experiments and later confirmed by Apollo 15 astronaut David Scott, who dropped a hammer and a feather on the Moon and observed they fell at the same rate.
However, in the case of skydivers, there are other factors at play, such as air resistance (drag). When a skydiver falls, they encounter air resistance, which acts against the force of gravity. A heavier skydiver will typically reach a higher terminal velocity than a lighter one because they can overcome air resistance more effectively due to their greater weight. This could explain why one skydiver appears to be falling slower than others, but it does not mean that they are lighter. Instead, it could indicate that among those jumping, there are differences in body position, gear, or other factors affecting their fall.
In summary, the speed at which skydivers fall is primarily influenced by air resistance and terminal velocity rather than their weight in relation to gravity alone. Therefore, just because one skydiver is trailing behind does not automatically mean they are lighter; other factors must be considered as well.