Good find.
Still appears to observe client/attorney privileged, so it's on the up and up where that is concerned.
It was actually referred to Rosenstein, and Rosenstein referred it, as a matter of technicality, so any implication that Mueller is acting rogue or outside his scope, would be inappropriate too.
The issue is what they are doing is legal and not uncommon for this type of high stakes criminal investigation. The Constitution is not being violated, they are not breaking the law, Mueller has not gone rogue, it's not Gestapo (slingshot bob), etc. It's unnerving to be sure, and entertaining to some, but it's the secrecy that ultimately frustrates most of us. We're using to getting to know everything immediately.
Having read up on the tactics they have to use to get at organized white collar criminals who have a history of hiding their misdeeds with money and expertise, I would not doubt it's related for a second either I suppose.