introductions

last night at volleyball i introduced myself to this japanese girl.

me: hi, i’m mike.
japanese girl: ah, i’m atsuko.
me: oh, you’re japanese!
japanese girl: yes. and you are?
me: i’m japanese too.
japanese girl: what?? you are? no…
me: …
japanese girl: you must be japanese american.
me: …

why do i keep getting this reaction from japanese people? am i not good enough to be in your club?