English version doesn't really capture Korea's honorific culture that well (but honorific language is hard to portray as its not really grammatically compatible with English). In Korea, you usually would use 존댓말 jondaenmal (honorific speech) to someone older than you (unless you have an established close bond or are chill siblings; Eunpa doesn't use 존댓말 really, but he does use the honorific title of "hyung"), and that isn't just using more polite words, but rather an entire integrated grammatical system where verbs are conjugated differently in respect to the hierarchy.
So in the Korean version, Ian will sometimes lower his speech to 반말 banmal (casual/informal speech), and it's a way of linguistically making himself on Eunsan's level or putting himself in closer proximity to him relationship wise. In the rink scene, he doesn't just call Eunsan by his name, but he also uses banmal. That's why Eunsan was EXTRA irritated. Ian lowered his speech to provoke him haha.
So it can be a bigger deal haha
Honestly, they acted like they had this huge ass age gap that I just automatically thought it was 4-6 years, and I never realised it was just 2 years