Meaning?
The hopeful logic being that he had heard through the legal grapevine (clerks) which case materials were being reviewed by which judges, and concluded that things were not going in favor of his argument before SCOTUS.
From what I recall this was not widely reported, in fact only one obscure law journal reported the resignation at the time it happened.
Of course it could also mean he got a great job offer from some DC firm based on his brilliant argument before SCOTUS.
Just a rumor.