Printers use cyan, magenta and yellow because printing is a subtractive process. It's the complement of the additive RGB that monitors use. For example, cyan acts as a filter for red, so a combination of magenta and yellow filters out everything but red and thus appears red. Ultimately, the difference is in whether something emits light (a monitor) or has to reflect light (a white piece of paper).

You're right in that what we're taught is often incomplete or misguided. Teachers are fallible. But as a child you assume their authority implies them being correct. I reckon seeing through that illusion is an important part of growing up. And to me, part of us growing up as humanity must involve not having to rely on the authority of governing bodies.