The internal configuration for the PMDG 777F surely has the plane correctly set as Cargo.
But, if you made some edits to it, or you downloaded a pre-made configuration made by someone else (no longer required, since the plane is internally supported since a long time), your custom configuration will take precedence over the GSX internal one. You can check the airplane configuration to see where GSX is taking its data from.
In any case, nowhere is indicated GSX removes the catering option, just because it's a Cargo plane so, it's entirely normal you'll still have it.
It's not very clear what do you mean with "wrong GSX vehicles". The only different vehicles will be the passenger Stairs, which will be replaced by Cargo stairs in Cargo airplanes, but the rest of the vehicles will be the same.