It's hard to justify how average citizens could be unaware of the Force. Surely a documentary would be made at some point about the Jedi, who supposedly had such an important role in the Republic. Surely there would have been some sort of scientific investigation into the claimed abilities of the Jedi. Surely there were cameras to record their supposed feats during the Clone Wars and broadcast them to the masses. The only real way to make sense of Han's statement is that the Empire had been suppressing the media and any and all information about the Jedi for at least his entire lifetime.