Burials
Of course, I know nothing for certain, and don't have all the details the scientist has.
I don't know if they've found many skeletons with whistles, or one. I do know that at the funerals of loved ones that I have attended, any number of small, beloved items of no significance to anyone else have been buried with them. A stuffed animal. A favorite photo.
For all we know, those whistles belonged to the skeleton's children.