If you take the story that Ben tells Luke about his father and the traitorous Darth Vader, who was a pupil of his, then I think you begin to understand the wider story that has been passed down through the galaxy: Darth Vader betrayed and murdered Anakin, and helped the Empire destroy all the other Jedi.
Therefore, Owen does have additional knowledge that most people don't -- knowing that Anakin was a troubled soul and dangerous Jedi that turned on Ben -- and perhaps even he knows that Vader is in fact Anakin underneath (or maybe this show allows them to learn that).