You probably tracked it from the chickens to the geese. Just because they don't come into contact doesn't mean it couldn't have traveled to them on your clothes, shoes, feeders, feed scoops, etc. You'll need to treat the geese too.
Just so you know this is likely caused by mycoplasma. If it is, all affected birds will be carriers for life and it will flare up whenever they are stressed, such as during a molt. They will also pass it to any new bird they come into contact with. You can never sell them to another person or you would be spreading the disease to their flock. Also, this disease can pass through the egg to the embryo inside, meaning hatch rates will go down and chicks and goslings that do hatch will likely hatch already infected with the disease. This means you can never sell your eggs to others for hatching, either, because you would be passing on the disease that way. You may want to cull one bird and send it off for necropsy so you know for sure what you're dealing with.
Sorry you are experiencing this. I went through it once myself and opted to cull my flock, as that is the only way to really get rid of it.