I’m pretty sure this design for trackballs dates back quite a bit before the Atari trackballs he was looking at for inspiration. You’d have to go do a patent search to figure out exactly who invented it and when.
https://www.google.com/patents/US3625083
Military tech historians note that the trackball was in use much earlier than this for radar tracking systems, but it was kept in secret.
About 5years later when mouses started to become popular because popular PC software began mouse support, it really didn't seem that novel by then.