Tl;dw - Unlike China and Japan, medieval Korea followed an extreme school of Confucianism that emphasized hierarchy and age over practicality. After WW2, the South Korean ~~dictatorship~~ government used this tradition to cement their own power. The video argues that these have made South Korea an extremely hierarchical, and in particular, sexist, society. A video game's refusal to sexualize a female character for their (mostly male) audience was thus seen as an attack on the system. A female artist at the studio was accused of being a 'radical feminist', and either fired or resigned to appease fans.
Edit: As Denjin pointed out, it should be Ming Dynasty and not Tang Dynasty.
I don't think that's the meaning OP is going for. In philosophy, idealism is the position that ideas exist independently of materials, or even that ideas are the true reality and the material world is either false or just a reflection of it. Many religions argue for some form of idealism.
Materialism, in contrast, is the idea that the material world is the primary one, and that ideas are at best descriptions of materials. Marxists and physical scientists hold this view. Finally, dualism is the idea that there is both a material and an ideal (i.e. 'of ideas', not 'perfect') world. Descartes is probably the most famous proponent of this school.
In the modern age, pretty much all serious thought accepts materialism, often implicitly, to the point that the material world is often called the 'real world' or even 'the world'. But this was not always so, and there are still relics of idealist and dualist thinking.