In an earlier post, Q said to think in terms of leveraging. Mueller nay have been handed a mission by Trump in return for not going to prison.
So Mueller was forced to do the right thing.
Or at least, that is our current guess.
I wonder why Q is emphasizing that Mueller could never have been FBI Director again, so why did Trump "interview" him for the position? That smacks of Trump and Mueller setting up this Sting all along.