I think the reasoning for the scene is: Vader and Palps both know that it was Skywalker who destroyed the Death Star and they both want rid of him. But there is a disturbance in the force, Palps has a premonition that things are kicking off somewhere in the galaxy, Luke has just met Yoda and that is like a pulse vibrating through the web of the Force, this is why Palps has this conversation with Vader, remember Vader tells this to Luke in ROTJ. Palps has forseen that Luke could destroy them.

My thoughts ??