WARNING GRAPHIC
I think Nate got insider info from LEO on the ground. He has been first responder (or someone on his team) on nearly every event in this case. I think he may have spoken too early - not realizing that the "dismemberment" part wasn't being released yet. It could be someone's interpretation of when they removed the bones, when it was an artifact of stirring burning the body. I do think that LEO searching in the firepit is more evidence they were looking for missing pieces of bone or teeth. We know 1 body was burned (we assume that to be Tylee) and the burning would happen in the firepit & CD confirmed burning that day.
It makes sense to me that whoever did the burning might try and stir the fire to get it to burn hotter - especially over specific evidence they would want to hide, destroy, or cover up.