You mention "brain fart". There is certainly a long history of pilots selecting the wrong lever, or wrong switch. So, it is possible the pilot who denied switching the fuel off thought he had switched something else.
If he was trying to do something else, he would have called it out. E.g. an audible “gear up.”
In my view it would be quite hard to move them by accident, and probably not possible to move at once.
It would be interesting to know if the plane has any other switches of the same type, that are routinely activated.