Can an american be a manga-ka

My nationaly is american. my race is human. My mother is consider black, and my father is half chinese and black with a picture of his mother as proof. So I was on and they severely crush me when i told them i was a manga-ka in a post they said simply i can't be a manga-ka because i was an american. i been studying japanase as a way to try and better relate to their style of comic book art. I thought the word manga ment comic and the ka added the expertise in that feild signaling you as a comic book artist in japanese. But they told me im just a comic book artist. Now it might seen insignificant but it hurt that because they said because im not japanese i can't be a Manga-ka and they will laugh at me for calling myself one. thats like telling Jin because he's chinese he can't be a rapper he only a spoken word poet. So my question is some one who is japanese. tell me is it truly impossible for me to be a manga-ka simply because im not japanese. I have to only be known as a comic book artist?