I don't know whether it is a four class 777, but there is a difference between using a plane in a four-class layout and offering four-class service. Usually (always ?) when a four-class plane is substituted for a three-class plane on a three-class route, F service is not sold or provided. If the F seats are used, it is normally to provide J service (although you are seated in F seats).

As I said earlier, if it is a four-class plane, whether the F seats are opened up and who gets to sit in them can be a bit unpredictable. Status helps, but is not the only reason to be given an F seat.