It would not surprise me if McVay looked at Stafford and his age last year and then looked at Mayfield and thought to himself "it's a dropoff but boy he sure is younger plus has some upside." I mean I was thinking that maybe he'd be thinking that and posed that question this past offseason here.
In the end the contract was probably not movable for them. That's the thing I'd cite as the most obvious reason it is unlikely they tried to move him. Because for example it is possible that a joking conversation was had here and there between Les and other GMs. Not him trying to move him, but other GMs calling to see if there was a QB available and maybe some rudimentary conversations on the cap gymnastics that would be required.
And maybe this dipweed knows of some conversations, one of whom may have been his Big Daddy Belicheat. I would have to think the Pats would make that phone call after the season ended or sometime around that, given their QB situation. And Les isn't lying to deny he tried to move him.