That is so interesting, Hellene. I have never seen an eaglet do this, although adults bring in nesting material even after the eaglets hatch-- often it is nest lining material which may be added to cover the left-over prey remains and perhaps deter flies. As has been said, they "sweep the dirt under the carpet."
In this case I assume that you did not see the eaglet return to the nest with the material. Perhaps it was exercising an instinctive behavior that will later become necessary for survival once it must build a nest of its own.
Maybe you have researched this and have found references to like behavior in eaglets? If not it will be interesting to know if it has been documented previously. We can learn a great deal by observing eagles "live" from the ground. A nest camera tends to provide a more intimate but also much narrower view of their activities.