Woooow please don't use that word if you don't know what it really means. Gaslighting is a serious manipulation tactic used to undermine someone's sense of reality, and using it in this context just makes you look ignorant.
That said, i did look through the chapters, and they dont use Dong-gu's pronouns once, so there is definitely credence to what you say with the honorifics. On the other hand, looking up the name itself, Dong-gu is a korean male name. The character is clearly also drawn different to other girls in the story, so i think its perfectly understandable why people would be confused about the gender. I personally still think they're supposed to be a guy, but until we get much harder proof than one greating that could have been missed in translation, who knows.
Its completely understandable to get dong-gu's gender confused. But the way op was talking as if it make nooooo sense whatsoever to be confused abt their gender when the author is probably being ambigous ON PURPOSE. Acting like ppl are crazy for having a reasonable confusion or assumption is GASLIGHTING. -_-
Disagreeing with someone about the gender of a fake character doesn't equal gaslighting. Idk about your experiances in life, but i have been seriously gaslit a lot in my life and it makes me unable to have confidence in my own objectibe reality sometimes. REAL gaslighting leaves a lasting mark on one's psyche.
I reread op's comment and in no way can i say that they are trying to make you feel crazy; they just said they think its concerning that people jump to the assumption that that character is a girl because theyre skinny.

Seeing a concerning amount of people question the purple guys gender like have you ever seen a high school boy before?? Yeah yeah I get it not every kid is the same BUT so many of them are lanky asfffff theyre basically twigs because so many of >those< guys also have pretty fast metabolisms- theyre not necessarily feminine