But Rick specifically says to Morgan it's been 1 year since they last saw each other.
That doesn't mean it's been exactly a year and a day. It could be a year plus several months. Or Rick could be wrong about the amount of time elapsed because he's barely slept. Why does that matter?
As for the hitchhiker being dumb because he's screaming, we don't know that he screamed as a matter of habit. He saw salvation and it was driving away from him. Wouldn't anyone scream in desperation?