I think the author is giving the FBI way too much credit by expecting them to document this. Whether the intent behind taking it down was nefarious or not, I really doubt they would have documented the action.
Does the term WBS mean anything to you? Back when I worked on federally funded stuff, it was used to document every part of a project deliverable, down to the very last flat washer. While the software parts were more loosely specified than that I can tell you that the content of any public facing documents was scrutinized and edited by top level people before being posted.
It's more than that on the DoD things I worked on. Not only did the flat washer's presence have to be documented, you had to have a complete explanation of what standards and the supplier(s) for it. For a part like that, you can point to a document than someone has already produced that specifies the flat washer's properties. There was an occasion where a engineer had to draw up a specification for a post-it note because they were called for in a procedure that was supplied to the federal government.
I suspect there was probably an e-mail from someone (PR?) to "the web team" at some point -- something like "hey, please remove this sentence (...) from this page (<url>)".