They made a fancy PDF instead of just putting that information into the game. I'd be fine with that if this was a silly game jam project made in a weekend. This had a QA team of more than ten people.I think the game is meant to be a little obtuse on purpose, but at least include the readme in the game files!
Some of it is intuitive. Mouse to select paint tools. WASD to move. Others aren't. Unless I looked at the readme, I wouldn't know pressing x changes the camera angle. (The readme also displays arrow keys for changing the camera angle. It means page up and page down.)