He may be thinking that the dealer put the flop with the stub, not the muck. Or that the flop was mixed with the muck which was also mixed with the stub.
However, if the stub is intact, I would never allow mucked cards to be reintroduced into play.
With your example about the Q on the original muck, it is possible, but frankly, no one will ever know, and under randomization theory, it could just as well be that the remaining queens were in the stub and had not yet come out. But if the remaining queens were in someone else's hand(s) that had been discarded, then the queens should have never come out no matter what, and in theory, other players at the table will know this (and you'll never hear the end of it).