It is, as far as I know, the first ever Marvel Comics movie with a black superhero. He is obviously black, and the comic book character happens to be an African prince of a fictional country, so I am sure that also fits in with the way it is being marketed. It is also worth mentioning that there has already been another African American superhero in a Marvel Netflix series, that being Luke Cage.

I believe the headline in question is due to this being the first film in the Marvel Universe depicting a black superhero, although it is obviously NOT the first ever such project.