From what i know, in korea "Kang" is a very common surname. Majority of the population also have have "kim", "lee", "park", "choi", so it's not unusual for him to not be suspicious, cause the probability that he met many people with the surname Kang before is high. I might be wrong, but many people explained this to me before so i take it as a fair explanation.
Also from what I know, in Korea men are very touchy with their buddies so probably didn't think of that. But you are right about the lying about going to the station, like come on yeonwoo you have had enough reality checks you need to be more aware
Haesol and haesoo got the same type. Also why did yeonwoo ignore the signs? The boy put his arm around him, nothing. Lied about going to the station, nothing. Name Kang haesoo? No questions asked. Come on bro (⊙…⊙ )