As
ESpen36 said, non revs do not need to use instruments to be in the front. They clear into the highest cabin available.
Another possibility, albeit less likely, Is that the gate agent operationally upgraded people. If coach is oversold then they will move people to a higher class in order to not IDB them.
Normally, they will leave the front cabin open. I've been on a 77W from Dallas with a reasonably full coach load and only 4 of us in the 52 seat business class cabin.