Bad example, because Bach's authorship of this piece is questionable
Weeeell. It's questionable in the sense that "Shakespeare"'s authorship of his plays is questionable. But just as no one has come up with a fully convincing alternative to William Shakespeare of Stratford, no one has come up with a fully convincing alternative to JSB writing 565. It has stylistic quirks, yes - but should that be surprising for "J.S. Bach the Rebel"?
There's a big gap between questioning the attribution of one piece to Bach and attributing all of Shakespeare's plays to someone else. For someone with a big body of work, there's always some debate around the edges. (For example, people now think Shakespeare was the co-author of a play about Edward III.)