LOL!
I don’t know if this is a thing outside of Kpop. https://www.youtube.com/results?search_query=is+the+butt+one+or+two
There’s logic on both sides and I don’t think there’s a word for butt cheek in Korean. There’s one nose, but two nostrils, one chest, but two breasts and it’s a ‘pair’ of panties!
The Korean word for butt 엉덩이 is eongdeong-i is so cute when used by the girls. And what’s especially funny and cute is those who say the cheeks can’t be moved separately. Guess they’ve never been to a strip club!
Personally, I’m in the two camp with Kirby Buckets and Tri-butt! https://www.google.com/search?q=tri+butt+kirby+buckets&tbm=isch&sa=X&ved=2ahUKEwjMqITFn5KAAxXiK30KHSBfA6YQ0pQJegQIDBAB&biw=1455&bih=990&dpr=1.1