The video is good. I think it will answer your question if you look at it again. The ball in the merry-go-round analagy actually travels in a straight line, but the perception is of a curve ball due to the rotation of the merry-go-round. Think of an air mass of moving in the same very simplified way, and don't over complicate it for the purposes of passing the exam. When you are flying this won't really come into your thinking, then, 10 years later, on pprune there's be a question mentioning Coriolis, and you'll think "Hey I remember that, what was it again?".