In the scene where Truman is going to work and notices the homeless man to be his father, they cart the father off and then make him reappear later in the show on purpose. Why was he dressed as a homeless in the first place?
He dressed like that to sneak past the rest of the cast. His appearance wasn't part of the in-universe show, but his attempt to write himself back into the show by showing himself to be alive. (And not to derail the show as I originally misremembered.)