Did he comprehend the significance of the Empire’s demise, or how insane it was the Rebel Alliance destroyed the Death Star not once, but two times?
Probably not, but one would think someone brought him up to speed on the story beats he needed to know before filming.
Not knowing anything about the sequel trilogy for the role is, presumably, not a big deal — although one has to imagine what was going through Werner Herzog’s head while filming The Mandalorian.