I hate when movies/shows reveal that two characters were actually the same person the whole time. It’s such a cop-out and feels like such a waste of time. The only way it works, I think is:if one of the characters was a real person who had passed away -and they dropped hints that they might be a figment of his…

I can understand your frustration, but almost every artist these days has a sketchbook on gumroad. It’s common knowledge within the illustration community. It says PDF pretty clearly, but maybe he just added that to the description after the fact?