I think he meant that you might fail if you went wild and turned it into a jazz bash.
Ah. OK. I failed the Bach I played for my grade 8, for possibly that sort of reason. It wasn't a jazz bash, but I played the C minor P&F, book 1, and decided to make the prelude very dramatic - it's a sort of moto perpetuo in all semiquavers in both hands until near the end. There are no performance direction in Bach, so I felt justified in doing this, and was upset that, seeing as I played the prelude note-perfect (a few wrong-note slips in the fugue) and I'd entered myself, including my qualifications as the applicant so I thought he ought to have given me the benefit of having played the prelude correctly "as intended". I started loud and very even staccato in both hands with no extra accent on any notes, like a machine, kept this up for about three lines, then gradually brought it down, as though I were shutting the door on this machine room, and then brought it back up again and beyond the point where I started it, until I could imagine the strings actually colliding with the intensity, keeping the staccato strong and very even, and the point at which it could go no further without the piano exploding was the climactic chord, after which there was the fast flourish (cogs and springs flying out of this machine>) and then the grandiose ending. I felt very proud of it.
Unfortunately my examiner didn't like it. He said it was far too aggressive an approach particularly with such a bright instrument (well, I couldn't have anticipated the instrument, I took the exam in a different city), and that there was no phrasing at all (er, that was the point). I was the last person he had that afternoon and maybe he already had a headache. However, he seemed to forgive me later as I followed this exam with grade 2 viola and got a distinction.
Maybe what I did was the equivalent of a jazz bash