Basically, you're not going to say and do the right thing, if you're raised by wolves in the woods, no matter what genes you contain. It is learned.
So then whether it's acting its just a question of how deeply is the learning integrated into your personality and how it aligns with your so called temperament.
Arguably, for anyone, it always is just playing a part. Japanese seem to get this point better than some, so tend to keep in character for longer.