Some childrens tv shows or media programs stating incorrect information does not make it correct. Additive primaries are RGB, subtractive primaries are CMY. The idea that RBY are primary colors is a popular misconception, but is incorrect. It has it's roots in art classes prior to proper scientific investigation of color, light, and modern technology. If your goal is art history, then yes, people in the past incorrectly believed that the primary colors (both additive and subtractive) were RBY. They were wrong. Just as people believed the earth was flat, yet were wrong.