I'm interpreting this as the FBI putting a coda on the whole story and a tacit way of saying they won't be looking at the Laundry parents for any charges such as obstruction of justice which a lot of people want.
Why don't they release the contents of the notebook? Maybe he has some artistic drawing skills and drew some Muppets or something. On a serious note, nothing has been shown except a van. No Gabby Petito body and no Brian Laundrie bones or notebook.
Some just don't trust the media, it's from years of lies maybe?!?!