The writer/director of the short explained the killer's story in an interview: though he tried to be a sitcom dad it wasn't meant to be, and implied that his killing spree was his way of getting revenge. Well, the killer's face pops up one last time at the end of the introduction, indicating that he's not quite dead after all. And whose head does his face appear over at the very end? The show's main sitcom dad. Whatever that imagery implies, it seems he got what he wanted in the end.
Katie Adkins and the doctor who catches Intronitis are still aware even as they're forced to smile and pose. What must have a floating credit in front of you be like? It's the last remnant of your old self, a name only you know but no one else will call you by. And you can never make it leave, even if, like in Katie's case, the credit makes you easier to find.