Was the employee's attendance to the luncheon mandatory? If yes, I would pay the employee. If it was voluntary, I would not pay the employee.
and there is "voluntary" and then there is VOLUNTARY (really mandatory but don't want to pay them). Make sure no pressure is put on the employee or that important information/training isn't missed and held against them. Or "voluntary" is really VOLUNTARY
"Inconceivable" - "You keep using that word. I do not think it means what you think it means."