I think so. Maybe not the direct quote, but I do recall reading that Strzok had "conditions" attached to accepting the assignment with Mueller, and one of them was retention of declassification authority.
I suppose there is a disclosure aspect to - Strzok could selectively disclose to team Mueller, with the intention being to color reality in order to provide justification for criminal charges or a recommendation to impeach.
Like you said, the declas-on-the-spot authority (or classify eternally) is the smoking gun. I also think this proves the Palpatine’s Revenge chat as legit.