Your video clip says that Korea suddenly raised the naming issue in 1992.
However, the 'East Sea' has been a famous name in East Asia for over 2,000 years.
In contrast, Sea of Japan never used the name before the 18th century.
After Japan invaded Korea in the early 20th century, Japan tried to spread the name internationally.
The fact was that the International Hydrographic Organization (IHO) called this sea the Sea of Japan in 1929. During the colonial period, Korea could not insist on any rights against Japan.