It wouldn't be smart to lay your cards on the table w/Mueller, especially if you were unsure as to his trustworthiness. However, if he was a secret patriot, in with Q group, biding his time, why would he need to meet with Trump beforehand? This tidbit as to eligibility would have been an unnecessary tell.
It would seem that Trump gave Mueller an ultimatum, knowing he was going to be appointed (we know all) - "Do this investigation right, and you'll walk", while simultaneously accounting for, and planning for the possibility of him running cover just like he did in the past.
Similarly, Mueller may not have made up his mind until somewhere in the middle of it, but who knows ;/
Love you Q