Some times I will see a hen do the same thing with throwing a leaf or hay or whatever it may be, I just figured that was their
way of making the nest more comfy around them.
Our hens do the same thing, what is surprising is that we hardly ever get a broken egg. I have watched the hen stand up
drop the egg on the hard nesting box (since they pushed out the material) did not break, when you get your first egg and go
and crack open you will see how hard it is to crack...