Where do you get this from? You have to pull up the switch with two fingers and move it to the other position and put it back in. This doesn't seem to take more than a second if deliberate.
To me, it points to a Germanwings-style sabotage. And the "I didn't do it" seems to be a lie. Not very confident in it, just the likeliest to me. Though one can ask why not just push the nose down instead. Maybe he thought that's too easy for the other pilot to counteract. The fuel switches are more out-of-mind and more startling to change.
