Apparently there was some doubt in the past as to whether Bach had written it. I have, coincidentally, a Dover edition of various preludes, toccatas, fugues, and fantasias that were not believed to be written by Bach when Dover published other volumes of Bach’s organ works. The famous d minor toccata BWV 565–apparently he wrote at least one other d minor toccata-fugue pair–is included.
It’s possible that Bach transcribed another work for organ. That would explain why it doesn’t ‘sound like Bach’ to most of us but still has some of his character in it. He did this very often, and for two reasons:
His elder brother and teacher didn’t want him to study composition, so his main method of learning when younger was to transcribe or copy works by previous masters in secret.
The original piece was an orchestral work, possibly Italian, that he wanted to perform. However, certain points in his career he didn’t have sufficient forces at his disposal to form the chamber orchestra required. The next best mode of performance would have been organ, so he rewrote the piece for organ in order to play it.
I have heard both scenarios cited in reference to BWV 565 but never with much evidence one way or the other. I’ve also never researched that piece myself, so there may be some.