Not just "from a certain point of view." They were objectively attempting to carry out a coup d'etat against Palpatine by removing him from office by force, and by suppressing the authority of the Senate and of the courts because of their (accurate) belief that both were under Palpatine's effective control. The Jedi determined that the organs of the democratic state were no longer capable of functioning, and so they sought, temporarily, to seize control of the state until such time as Palpatine's influence could be eliminated. This is objectively a coup. Now, whether or not it is a justified coup is the relevant question. I of course think it is. But its nature as a coup remains. Totalitarian regimes often change their "origin stories" without acknowledging such changes. (E.G., Stalin writing Trotsky out of Soviet history, or Orwell's "Oceania has always been at war with Eastasia.") Add to the that the simple fact that a galaxy with trillions upon trillions of people is necessarily going to be very diffuse and inefficient in how it distributes information, and it's not implausible that there would be a huge amount of disinformation out there. You say that like such people do not exist in huge, huge numbers. Anyway, the simplest explanation is that Han is speaking a bit inaccurately for the sake of brevity -- not that he thought the existence of the Jedi Order was a myth, but that he thought the Force and their alleged ability to wield it was a myth. People will sometimes simplify such things for the sake of brevity in conversation.