not too sure about how incorrect the artist's concept is, but we have to remember that Promixa Centauri is a red dward with about 1/10 the radius of our Sun.
Ah maybe when the article said the star is "bigger" than the Sun it meant "more massive." Which could explain the apparent contradiction, if it was more massive and smaller in radius. Of course then it would be denser than the sun, which would have to be the case for all of this to make sense.