Thrust Lever "Stuck"
One explanation for the Pilot to say -"its stuck, it wont move etc" is because the pilot has firmly gripped the 'Stray' No1 TL and is exerting too much of a sideways force on the lever thereby Jamming it in position.
A Flight Attendant on the manchester air crash was unable to open a door because he put too much inward force on the handle. The door handle then became jammed with brute strength. Under the circumstance I would imagine the force to have been way above his normal strength.
The same logic could apply in this case.
Retarding only one Thrust Lever
A BIA aircraft coming into land on runway 08L at Gatwick. The a/c was perfectly lined up with the r/w and on a clear night. The PNF then mentioned that Gatwick was using the Secondary runway. The PF then thought how can this perfectly lit runway be the 'Secondary' runway. He then manoevered the plane left to line up with the green lights thinking that this looked more like a 'Secondary' runway, and landed on the taxyway.
The PF here on getting the call 'Reverse number 1 only' could then have moved his hand off the no2 lever and concentrated on the no1 TL only.
This is just a thought and I guess we will never know the real reason why on touchdown both levers were not retarded. However there must be a reason.
Jim