Koreans themselves admit it.
In fact, in ancient times, South Korea was rich in grapefruit, but it was extremely bitter and sour and could not be eaten directly. The Korean emperor sent envoys to China, the hometown of honey pomelo, to learn planting techniques.
During this time, the emissary found that the villagers would make a kind of "honey pomelo tea" for the winter, and the villagers described drinking citron tea as a health preserving behavior. After the messenger learned, he brought the production technology of honey pomelo tea and honey pomelo seedlings back to South Korea. The sour and inedible grapefruit was made into the present "honey grapefruit tea" by the folk craft in China.
Of course, due to the different varieties of grapefruit, South Korea has also added high-sugar fruits (such as papaya and orange) to honey grapefruit tea to cover up the bitter taste and sour taste, and the taste is not pure citron tea.