Kinda like how hot dogs are made with a combo of beef, pork, and poultry (usually chicken) unless specifically labeled as all beef its no surprise a place like that would be using generic processed meats where something like that exists.
With that being said it looks to me like this is talking about like on their burgers having pork in them which is not unheard of. People use pork in meatballs to add fat and juice. Same way deer meat from a processor typically has pork added otherwise its too lean and gamey.
So its probably being done to make them juicier.
PSN ID: sled_dogs76
60" Pioneer Kuro Elite PRO151FD, Yamaha RX-V3900 A/V Receiver, Oppo DV983-H player. Coming soon: 2 Seaton Submersives from Mark Seaton