This is at least believable. If Trump knew there were no legitimate charges to be brought against him then the one peril was a perjury trap which Mueller's team is practiced at springing. So he didn't give Mueller that face-to-face opportunity.
OTOH, declassifying what would blow up the DOJ-FBI could turn even the Republican Congress against him. McConnell and others have surely informed him of congressional reality in that regard.
So, the still classified material becomes a fleet in being.