The objects created by the sim *before* you call GSX, are "Airport Services", and they are placed by the simulator, according to the Airport Services files we supply for each airport with GSX. As you can see on Swissport site:
https://www.swissport.com/en/networkThey do offer Handling at KBOS, so it's completely appropriate you could see Swissport there, and the way Airport Services work, they can be customized by parking TYPE and there can't be more than a single vehicle associated to each type, which means every parking type will have a different set of operators that will all match that airport, but they will be always the same, because that's how Airport Services work.
Only after you start GSX, they are chosen with more flexibility, possibly with a menu, possibly with an airport customization file, all things GSX knows, but the Airport Service system does not.