Yo we're only 4 chapters in what the hell is pink tb she'd go after high schoolers 💔

It's a mistranslation, try to read official translation. In the official translation Seju said "Funny coming from you, you even hooked up with a high schooler" it's Sumin who dated a high schooler. When Sumin said Sungji is a kid she wouldn't date her, Seju exposed her lie by bringing the fact that Sumin literally dated someone who is way younger than sungji (a high schooler)

Oh okay I see now, ty !