That just as simple as they actually never married and he left his girlfriend pregnant and raise the kid on her own
I'm guessing that at the time they were just dating and not married so he said "I'm her boyfriend", It might be that he got Kwons mom pregnant and dipped
That he was his mom's bf and then he disappeared leaving her and his son behind (for whatever reason) and now that hecame back he expects to see her like sir she ded
Is that who he came to see? The mom? Because he called her one name and then asked to see someone with a different name?
It's the "I'm her boyfriend" for me that better be a mistranslation because what could he possibly mean