Joseph: You're misreading the article. Jazz Marion isn't talking about a genre of music called blues. It would make no sense to say that 12-bar blues isn't written and is just interpolated by the performer. He's saying that about blue notes, which are not only sour and discordant but also often involve bent strings so that the note can't be represented in a conventional score.

The columnist may be talking about a type of music called "the blues," though that isn't clear. He definitely thinks there is a type of music called "blue music," and "jazz blues," but what he means by "blues" isn't clear. However, when he asks Marion about the blues, the latter replies in accordance with what the term means to him. Marion doesn't call the style of music blues; he calls it jazz.