To be clear ... I haven't been able to find any other information on this for verification and looking thru the OAN website, I don't see the story as the tweet would have you believe that it originated!
I don't know who Jack Posobiec is either or if he is a reliable source!?
I took the information as Mueller being upset with Piglosi calling Barr a liar and wanting to testify as to why Barr wasn't lying?