Panda and Po are the same person. It is basically showing Po from "Kung Fu Panda" as he ended up becoming an elder, many years after all three "Kung Fu Panda" movies were made. Skunk, Rabbit, and all the other animals in "Skunk Fu" are Po's students he trains in kung fu. It is also formal for them to call him "Panda" rather than "Po" as "Po" is rather something they would call one of their friends as opposed to a teacher. No wonder Panda and Po look so much alike!