The identity of Santa transcends one body, but his identity manifests in many bodies. If someone is dressed as Santa and you wave and he says "ho ho ho!" you say "hi Santa!" But if you wave and he says "leave me alone. My wife left me last night," then it is suddenly clear you are no longer talking to Santa, but instead to a guy dressed as Santa, but who is having a bad day. Just because Santa's identity transcends one body doesn't mean he isn't real. You can interact with Santa, and know when you aren't interacting with Santa.